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CODE SCANNER - Bosch Diagnostics

1. Diagnostic Connector Remove cover for testing Replace cover after testing Some vehicles require this cover in place for proper operation 4 Verify Ignition Key is ON and Engine is OFF wy 5 Put the TEST switch on ABS i D gt OS D Or P Gs EN A e 4 Noes BY X y S gt 6 Plug the Code Scanner into the Test Connector e The Code Scanner only fits ONE WAY into the test connector e The Code Scanner will not harm the vehicle computer Note The Code Scanner does not use all of the test connector contacts This is normal 7 Get the Code from the Flashing Brake Light e Count flashes to get the trouble code Flashes begin after 20 seconds or more The code starts with one long flash and is followed by several short flashes Count the long flash along with the short flashes to get the code number After a pause the code is repeated 87 Code 3 looks like LONG SHORT SHORT 1 So Da E 4 yv dis dis FLASH FLASH FLASH starts over Code 3 pause Code 5 looks like LONG SHORT SHORT SHORT SHORT 1 wae Ea B Ela Ea dis rN rN dis dis FLASH FLASH FLASH FLASH FLASH starts over Code 5 pause e The same code is flashed over and over again Note thatthe long flash helps you tell when the code is being repeated e Important The code may be flashed incorrectly the first time The code will be flashed correctly the rest of the time Count the flash sequences a
2. e Turn ignition key OFF e Remove the ECM fuse from the fuse block for 10 seconds e Replace fuse e Remove Code Scanner If ECM fuse cannot be located then e Disconnect power to the computer To do this Disconnect the positive battery terminal pigtail OR Open the in line fuse holder going to the positive battery terminal OR Disconnect negative battery terminal but this will also erase other items too such as digital clock settings and preset digital radio tuning e All the trouble codes are now erased from computer memory e Wait thirty 30 seconds 3 d SECO e Reconnect power to the computer IMPORTANT The computer has a learning ability to take care of minor variations in engine control operation Whenever you erase the computer memory by disconnect ing power the computer has to relearn various things Vehicle performance may be noticeably different until it relearns This temporary situation is normal The learning process takes place during warm engine driving 15 SATURN Use the GM method or proceed as follows e Observe all safety precautions See page 4 Warning Stay away from the engine cooling fan It may turn on during this procedure e Turn ignition key ON but DO NOT START THE ENGINE E e Put TEST switch SOS on ENGINE SE SS e Plug and unplug the Code Scanner into the test connector
3. Reading ABS Codes Kelsey Hayes RWAL IMPORTANT Perform all steps in DIAGNOSTIC CIRCUIT CHECK before reading ABS codes 1 Take Safety Precautions e Set parking brake block drive wheels e Put shift lever in PARK automatic transmission or NEUTRAL manual transmission e Make sure ignition key is in OFF position 2 Verify ABS Problem Currently Exists e Turn the ignition key to the ON position but do not start the engine WARNING Stay away from the radiator cooling fan It may turn on e Wait 5 seconds and then observe the brake warning light Brake light OFF ABS computer does NOT detect a current problem _Do not proceed with this test A false code 9 will be stored in ABS computer memory if the code reading steps are followed when no faults currently exist Turn the ignition key OFF and stop testing Brake light ON An ABS problem currently exists At least one trouble code is stored in computer memory Go to step 3 and continue code reading procedure 3 Find the Computer Test Connector e Service manuals call this connector the Assembly Line Diagnostic Link ALDL connector It may also be called the Assembly Line Communi cation Link ALCL or simply test connector e The connector is located under the dashboard on the driver s side e The connector may be in full view or it may be recessed behind a panel opening e The connector may have a slip on cover labeled
4. Torque Converter Clutch TCC circuit intermittent fault 97 Information Flag 2nd gear circuit intermittent fault 98 Information Flag 3rd gear circuit intermittent fault 99 Information Flag 4th gear circuit intermittent fault Other Features Additional Code Scanner Diagnostic Features This section contains Relay and Solenoid Circuit Test You can switch on most of the computer controlled relay and solenoid circuits for checking relay operation or making wiring voltage checks Field Service Test Fuel Injected Engines Only A quick check of the fuel control system to verify proper operation Become familiar with Code Scanner use Section 3 before using the following procedures Relay and Solenoid Circuit Test Computer controlled relay and solenoid coils are commonly wired as follows e One side of the coil is connected to a source of vehicle battery power e The other side of the coil is wired to the computer Inside the computer housing is a transistor switch often called a RELAY COIL 12 volts or more zk Less than 1 5 volts RELAY ON Transistor action is shown using a switch RELAY COIL representation for Clarity d 12 volts or more dk 12 volts or more RELAY OFF COMPUTER driver The computer energizes the coil by using the transistor switch Transistor ON Transistor electrically
5. Barometric Pressure Sensor See MAP sensor for explanation Boost control solenoid Used on certain supercharger equipped engines This solenoid is normally energized by the ECM This allows the supercharger system to operate normally The ECM de energizes the solenoid during higher engine speed and load conditions to reduce boost pressure Brake switch Signal An input signal to the ECM indicating that the brake pedal is being depressed Vehicles with Cruise Control systems monitor the brake switch to determine when to engage or disengage the cruise control function The brake switch may also have a circuit Supplying power to the Torque Convertor Clutch TCC solenoid This connection ensures the TCC solenoid will disengage when the brake pedal is depressed see TCC definition C3 Computer Command Control The name for the GM electronic engine control system used on most vehicles built since 1982 CALPAK A spare tire for the ECM It is circuitry which can operate the vehicle fuel injectors in a limited fashion should the ECM malfunction The CALPAK is hidden behind an access door on the ECM The replaceable CALPAK module is only used on certain ECM s CAM Camshaft Position Sensor This sensor sends a frequency signal to the ECM Vehicles with sequential fuel injection SFI use this signal to synchronize the injector firing order Some DIS type ignition systems use this signal
6. Clamp open OR Information Flag Handwheel sensor circuit fault handwheel sensor output voltage is out of tolerance 68 Information Flag Line circuit grounded or open 69 Information Flag Line circuit shorted 22 71 Information Flag 2nd line circuit grounded or open OR Information Flag Cooling system high temperature engine coolant temperature is greater than 239 F 118 C 72 Information Flag 2nd line circuit shorted OR Information Flag Cooling system low temperature engine coolant temperature is less than 32 F 0 C 73 Information Flag 3rd line circuit grounded or open OR Information Flag Coolant sensor signal unstable coolant temperature sensor CTS indicates a change of more than 59 F 15 C instantaneously 14 Information Flag 3rd line circuit shorted OR Information Flag Coolant Transmission temperature sensor ratio error indicates a degrading coolant temperature sensor CTS if transmission temperature sensor TTS is working properly 75 Information Flag 3rd gear stuck on OR Information Flag Air temperature sensor signal unstable air temperature sensor ATS indicates a change of more than 59 F 15 C instantaneously 76 Information Flag 4th line circuit grounded or open OR Information Flag Throttle position sensor TPS to manifold absolute pressure MAP sensor
7. Code 23 looks like lp gt lp al al AN ALS PAUSE WO ASN FLASH FLASH 3 second pause FLASH FLASH FLASH then light stays on 10 Get More Codes if any from Flashing Anti Lock Light e Do this step after first code has been flashed and anti lock light is ON steadily e Do NOT turn ignition switch off Remove Code Scanner from test connec tor Then Re install Code Scanner into test connector The next ABS trouble code if any will be flashed in the same manner as the first code e Repeat this step until all trouble codes have been read The ABS computer can store up to 7 trouble codes 11 Turn Ignition Key OFF 12 Remove Code Scanner and Re install Connector Cover if supplied The computer system is now back to normal operation 13 Refer to ABS Code Meanings on page 79 Teves Mark Il Version A This completes the code reading procedure At this point you can either e Have your vehicle professionally serviced Trouble codes indicate problems found by the computer OF e Repair the vehicle yourself using trouble codes to help pinpoint the problem IMPORTANT Always follow vehicle service manual proce dures for any ABS repairs Erasing ABS Codes from Computer Memory Teves Mark Il Version A Erase codes from memory whenever you complete a repair or to see if a problem will occur again 1 IMPORTANT Trouble codes cannot
8. e Always wear approved eye protection e Always operate the vehicle in a well ventilated area Do not inhale exhaust gases they are very poisonous e Always keep yourself tools and test equipment away from all moving or hot engine parts e Always make sure the vehicle is in park Automatic transmission or neutral manual transmission and that the parking brake is firmly set Block the drive wheels e Never lay tools on vehicle battery You may short the terminals together causing harm e Never smoke or have open flames near vehicle Vapors from gasoline or charging battery are highly explosive e Never leave vehicle unattended while running tests e Always turn ignition key OFF when connecting or disconnecting electrical components unless otherwise instructed e Always follow vehicle manufacturer s warnings cautions and service procedures CAUTION Some vehicles are equipped with safety air bags also known as Supplemental Inflatable Restraint SIR system You must follow vehicle service manual cautions when working around the air bag components or wiring If the cautions are not followed the air bag may open up unexpectedly resulting in personal injury 46 ABS TIPS Useful Hints to Know When Troubleshooting ABS Systems Do a thorough visual and hands on inspection first You can often find the cause of many problems by just looking ABS systems rely on accurate wheel sensor signals Anything which inter
9. fault loss of 24X signal or extra or missing pulses in electronic spark timing EST signal OR Ignition system fault loss of High Resolution Pulse signal 37 Brake switch stuck on 38 Brake switch circuit fault OR Knock sensor KS open circuit problem 39 Torque converter clutch TCC circuit fault OR Clutch switch circuit problems OR Knock sensor KS short circuit problem 41 Cam sensor CAM failure OR Cylinder select error OR Tach input error no reference pulses during engine run OR Electronic spark timing EST circuit open or shorted to ground during engine run OR Direct ignition system DIS fault bypass circuit open or shorted to ground during engine run OR Ignition system fault loss of 1X Reference Pulse signal 42 Electronic spark timing EST circuit open or shorted to ground during engine run OR Direct ignition system DIS fault bypass circuit open or shorted to ground during engine run OR Fuel cutoff relay circuit open or shorted to ground 43 Electronic spark timing EST circuit low voltage detected OR Electronic spark control ESC circuit problems 44 Lean exhaust indication oxygen O sensor voltage stays low after one or two minutes of engine run Left sensor on dual sensor engines 45 Rich exhaust indication oxygen O sensor voltage stays high after one minu
10. longer pause aly NUNS NS SES FLASH pause FLASH FLASH longer pause y ye S PAUSE ASAS FLASH pause FLASH FLASH even longer pause then start over again Example of code series 12 and 24 al gt S PAUSE 79787 FLASH pause FLASH FLASH longer pause aly NUN Av PAUSE WOW FLASH pause FLASH FLASH longer pause als ale G SO FLASH pause FLASH FLASH even longer pause then go to next code ly gt Ne ae w Se On Ore PAUSE SS ERE FLASH FLASH pause FLASH FLASH FLASH FLASH longer pause Ny y lp gt al 2 P e AE ASS SS FLASH FLASH pause FLASH FLASH FLASH FLASH longer pause ale als lp tp Sp Ip SANT PAUSE BTN ANTS FLASH FLASH pause FLASH FLASH FLASH FLASH even longer pause then start all over from the very beginning e Acode 12 is always sent even when the computer sees no problem This tells you the computer diagnostic checks are working properly e All codes are two 2 digits long 9 Turn Ignition Key OFF 10 Remove Code Scanner and Re install Connector Cover if supplied The computer system is now back to normal operation 11 Refer to ABS Code Meanings on page 74 Bosch 2U Version C This completes the code reading procedure At this point you can either Have your vehicle professionally serviced Trouble codes indicate problems found by the computer OF Repair the vehicle yourself using
11. 14 ABS System functional 4WD service brake not applied This code indicates that the anti lock brake system as installed on a 4 wheel drive vehicle is functioning normally As indicated above this code should appear without the service brakes applied 15 ABS System functional 4WD service brake applied This code indicates that the anti lock brake system as installed on a 4 wheel drive vehicle is functioning normally As indicated above this code should appear with the service brakes applied If with the service brakes applied the anti lock lamp continues to indicate a code 14 it is likely that there is a problem with the stop brake lamp switch circuit Assistance is available under the diagnostic chart for diagnostic trouble code 81 21 Right Front Wheel Speed Sensor Circuit resistance is incorrect This code is indicative of high resistance in this particular wheel speed sensor circuit The resistance of the wheel speed sensor may be out of specification or there may be loose corroded or dirty connections in this circuit 22 Right Front Wheel Speed Sensor Voltage Output is incorrect This code indicates a problem in the wheel speed sensor or its associated tone toothed wheel Check for the proper air gap between the wheel speed sensor and tone wheel missing or broken teeth on the tone wheel a loose improperly mounted or mis adjusted wheel speed sensor An intermittent connection in
12. 3 times within 5 seconds e All the trouble codes are now erased from computer memory e Turn ignition key OFF e Remove Code Scanner and re install connector cover if supplied NOTE e The engine control computer is usually called ECM Engine Control Module or PCM Powertrain Control Module in the vehicle service manuals e Information flags and Intermittent codes may not by erased using this procedure The presence of these codes will not cause any driveability or future self diagnostics problems Code Meanings Note e Code meanings can vary with vehicle model year engine type and options e Ifa code number has more than one definition listed note that that only one definition applies to your vehicle Consult service manual to get the specific definition and troubleshooting procedure for your vehicle e Follow vehicle service manual procedures to find the cause of the code Remember 1 Visual inspections are important 2 Problems with wiring and connectors are common especially for intermittent faults 3 Mechanical problems vacuum leaks binding or sticking linkages etc can make a good sensor send an incorrect signal to the computer This can cause a Trouble Code 4 Incorrect information from a sensor may cause the computer to control the engine in the wrong way Faulty engine operation could even make a different good sensor send an incorrect
13. TPS signal are zero volts 55 Transaxle temperature sensor failure 56 Information Flag Generic Field Effect Transistor FET driver failure 57 Information Flag Powertrain Control Module PCM computer circuit problem non volatile Random Access Memory RAM failure 58 Information Flag Battery voltage unstable battery voltage changes more than 3 volts instantaneously 61 Information Flag Powertrain Control Module PCM computer circuit problem Programmable Read Only Memory PROM failure OR Information Flag 6X Signal fault 6X pulses do not occur between each reference pulse or a 6X pulse does not immediately follow a reference pulse Possible open or intermittent in DIS module harness 62 Information Flag Powertrain Control Module PCM computer circuit problem interrupt failure 63 Information Flag Powertrain Control Module PCM computer circuit problem Random Access Memory RAM failure OR Information Flag Option check sum error flag will be set if tire size and options do not compare with those stored in the powertrain control module PCM 64 Information Flag Powertrain Control Module PCM computer circuit problem Electrically Erasable Programmable Read Only Memory EE PROM failure 65 Information Flag Ignition voltage problem too high or low 66 Information Flag Clamp shorted 67 Information Flag
14. loss or damages suffered through reliance on any information contained in this manual or misuse of accompanying product Bosch reserves the right to make changes at any time to this manual or accompanying product without obligation to notify any person or organization of such changes 98
15. output failure OR Mixture Control M C solenoid circuit voltage too high 55 Electronic control module ECM computer circuit problems ECM failure serial bus error SAD error or fuel lean malfunction OR EGR Solenoid No 3 failure 56 Corrosivity add coolant OR Port throttle system vacuum sensor problems OR Quad Driver B fault 57 Boost Control problem 58 Vehicle anti theft system VATS problem OR Transmission Temperature Sensor TTS short circuit problem in sensor or wiring OR Transmission fluid temperature high 59 Transmission Temperature Sensor TTS open circuit problem in sensor connector or wiring OR Transmission fluid temperature low 61 Oxygen O sensor degraded OR Port throttle system error OR Cruise control problems vent solenoid circuit OR Air Conditioner A C system performance problems 62 Gear switch circuit problems OR Oil temperature sensor signal voltage is high Corvette OR Cruise control problems vacuum solenoid circuit 63 Manifold absolute pressure MAP sensor signal voltage is high OR Small EGR failure OR Right oxygen O sensor failure dual sensor engines OR Cruise control system problem 64 Manifold absolute pressure MAP sensor signal voltage is low OR Medium EGR failure OR Right oxygen O sensor lean condition indicated dual sensor en
16. voltage out of range flag is set if TPS and MAP voltage readings dont agree with internal relational tables stored in the powertrain control module PCM 17 Information Flag 4th line circuit shorted 78 Information Flag 4th gear stuck on 79 Information Flag Torque Converter Clutch TCC circuit grounded or open 81 Information Flag Torque Converter Clutch TCC circuit shorted 82 Information Flag Transaxle temperature unstable 83 Information Flag Transaxle temperature low OR Information Flag Low coolant coolant switch opens for 20 seconds with engine running 84 Information Flag Brake switch stuck open 85 Information Flag Brake switch stuck closed 86 Information Flag Engine speed invalid 87 Information Flag Torque Converter Clutch TCC hold circuit grounded or open 88 Information Flag Torque Converter Clutch TCC hold circuit shorted 89 Information Flag Master relay stuck on 91 Information Flag Assembly Line Diagnostic Link ALDL serial communication link interrupt 23 92 Information Flag Clamp circuit intermittent fault 93 Information Flag Torque Converter Clutch TCC hold circuit intermittent fault 94 Information Flag Master enable relay circuit intermittent fault 95 Information Flag Line circuit intermittent fault 96 Information Flag
17. 44 Left Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 45 Left Front Wheel Speed Sensor Signal Missing Checks for missing signal in the subject circuit 46 Right Front Wheel Speed Sensor Signal Missing Checks for missing signal in the subject circuit 47 Either Rear Wheel Speed Sensor Signal Missing Checks for missing signal in either of the rear wheel speed sensor circuits Note that it is impossible to determine which of the rear wheel speed circuits is causing the problem This code will set if the front wheels spin while the rear wheels are stationary 48 Any three Wheel Speed Sensor Signals Missing There are missing signals in three 3 of the four 4 wheel speed sensor circuits 51 Left Front Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 71 which has the same meaning 52 Right Front Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 72 which has the same meaning 53 Right Rear Wheel Hydraulic Pressure Reduction fault This code i
18. Dump valve is CLOSED not energized This valve has no effect on the brake pressure when it is closed Systems using two stage solenoid Solenoid is not energized Hydraulic flow same as described above ABS Braking Pressure Maintain Wheel speed signals indicate lock up is about to occur ABS computer takes first step in brake control cycle isolate wheel caliper cylinder from master cylinder maintain fluid pressure to wheel Master Cylinder To Wheel Isolation Valve CLOSED Cylinder Accumulator or Reservoir HYDRAULIC PRESSURE FLOW Isolation valve is CLOSED ener gized Pressure flow between master cylinder and brake caliper cylinder is blocked because of closed valve Existing pressure to wheel is maintained because hydraulic fluid is trapped between isolation valve and wheel Closed isolation valve also prevents any increases in master cylinder pressure from reaching wheel caliper cylinder Dump valve is CLOSED not energized This valve has no effect on the brake pressure when it is closed Systems using two stage solenoid Solenoid is partially energized Hydraulic flow same as described above ABS Braking Pressure Decrease Wheel speed signals indicate lock up is still about to occur ABS computer takes next step in brake control cycle decrease hydraulic pressure to wheel caliper cylinder Master Cylinder From Wheel Caliper or Cylinder Accum
19. Remove the HORN DM fuse e 1989 S Series Trucks Remove the ECM B fuse e 1990 92 G Series RWD Vans Remove the TAIL LPS fuse e 1990 91 R amp V Series Suburbans etc Remove the STOP HAZ fuse e 1990 93 S amp T Series Trucks Remove the ECM B fuse 3 Replace fuse Trouble codes are now erased from computer memory ABS Code Meanings Kelsey Hayes RWAL IMPORTANT Always follow vehicle service manual procedures for any ABS repairs 1 ECM Electronic Control Module Failure This code indicates an anti lock brake system control module failure or a mis read code 2 Open Isolation valve or defective ECM Electronic Control Module This code indicates an open circuit in the isolation valve or associated wiring The anti lock brake system control module may also have failed 3 Open Dump valve or defective ECM Electronic Control Module This code indicates an open circuit in the dump valve or associated wiring The anti lock brake system control module may also have failed 4 Grounded anti lock valve Reset Switch This code indicates a grounded circuit in the anti lock valve reset switch or associated wiring 5 Excessive actuation of the Dump valve during an anti lock stop On 2 wheel drive vehicles this code indicates probable failure of the isolation dump valve assembly On 4 wheel drive vehicles this code indicates either possible failure of the isolation dump valve ass
20. Scanner will not harm the vehicle engine computer NOTE The Code Scanner does not use all of the test connector contacts Also one Code Scanner pin may plug into an empty test connector position This is normal 7 Turn Ignition Key to ON Position but DO NOT START THE ENGINE You may hear some clicking sounds coming from under the hood This is normal WARNING Stay away from the radiator cooling fan It may turn on 8 Get Codes from the Flashing Check Engine Light NOTE If the light does not flash you have a problem which must be repaired before proceeding Refer to Diagnostic Circuit Check chart in vehicle service manual Count flashes to get trouble codes Code 12 looks like ON PAUSE ee FLASH pause FLASH FLASH FLASH 1 FLASH FLASH 2 Put 1 and 2 together code 12 Code 23 looks like al xp al ale als Se AE ASS ens FLASH FLASH pause FLASH FLASH FLASH e Each code is flashed three 3 times before the next trouble code is sent e After all codes are sent the whole sequence is repeated This continues until the ignition key is turned OFF so you can double check your code list Example of code 12 only als ale X PAUSE WI FLASH pause FLASH FLASH longer pause lp gt Se PAUSE 707 787 FLASH pause FLASH FLASH longer pause als ale X PAUSE IAS FLASH pause FLASH FLASH even longer pause then start over again Example of code series 12 and 2
21. Sierra Sonoma Suburban Syclone T Series Pickup Truck Toronado Trofeo Typhoon V Series Truck System 7or8 See note p 52 7or8 See note p 52 8 90 3 64 T 86 2 58 1 53 2 58 3 64 7 86 7or8 See note p 52 7 86 7 86 3 64 3 64 2 58 7or8 Seenote p 52 7or8 Seenote p 52 3 64 7 86 8 90 T 86 8 90 7or8 Seenote p 52 3 64 3 64 8 90 T 86 Model System Astro 7or8 Blazer 7or8 Bravada 8 Brougham 2 C Series Pickup Truck 7or8 Eldorado 3 G Series RWD Van 7 Jimmy 7or8 K Series Pickup Truck 7or8 Riviera 3 S Series Pickup Truck 7or8 Safari 7or8 Seville 3 Sierra 7or8 Sonoma 8 Suburban 7 or8 Syclone 8 T Series Pickup Truck 7or8 Toronado 3 Trofeo 3 Typhoon 8 Yukon 8 Page See note p 52 See note p 52 90 58 See note p 52 64 86 See note p 52 See note p 52 64 See note p 52 See note p 52 64 See note p 52 90 See note p 52 90 See note p 52 64 64 90 90 Model Astro Blazer Bravada C Series Pickup Truck Eldorado G Series Van Jimmy K Series Pickup Truck Riviera S Series Pickup Truck Safari Seville Sierra Sonoma Suburban Syclone T Series Pickup Truck Typhoon Yukon System 8 7or8 Seenote p 52 8 7or8 7or8 7or8 7or8 7or8 7or8 7or8 90 90 See note p 52 70 90 See note p 52 See note p 52 64 See note p 52 90 70 See note p 52 90 See note p 52 90 See note p 52
22. The voltage changes to 0 4 volts or less when the exhaust gas is lean high oxygen content The sensor only operates after it reaches a temperature of 349 C 660 F Outputs Electrical signals sent from the ECM These signals may activate relays or other actuators for control purposes around the vehicle The signals can also send information from the ECM to other electronic modules such as ignition or trip computer P N Park Neutral switch This switch tells the ECM when the gear shift lever is in the Park or Neutral position Then the ECM will operate the engine in an idle mode Pressure Con trol solenoid This solenoid is located inside certain automatic transmissions The ECM uses this solenoid to vary the internal line pressure as required based on engine load condition PROM Programmable Read Only Memory A small replaceable electrical component hidden behind an access door on the ECM The PROM contains permanent programming information the ECM needs to operate a specific vehicle model Included are vehicle weight engine and transmission type axle ratio and other specifics PS Power steering switch This tells the ECM when power steering is being used The ECM can prevent stalling on a small idling engine by watching this switch and increasing idle speed if power steering is being used Purge solenoid This device controls the flow of fuel vapors from the carbon canister t
23. VSS circuit no signal 42 Vehicle Speed Sensor VSS circuit signal noise 43 Information Flag Master relay open or grounded 44 Information Flag Master relay shorted 45 Information Flag Gear selector switch circuit problem no signal 46 Information Flag Gear selector switch circuit problem invalid signal 21 47 Information Flag Powertrain Control Module PCM computer circuit problem communication interrupt failure 48 Hold mode voltage is too low OR Information Flag Reference input intermittent or noisy missing or extra ignition reference pulses are detected by powertrain control module PCM 49 Information Flag Gear selector error signal 51 Information Flag Powertrain Control Module PCM computer circuit problem serial link data invalid 52 Hold mode stuck on OR Information Flag Battery voltage out of range battery voltage has dropped below 11 volts or has increased above 17 volts 53 Hold mode stuck off OR Information Flag ESC Knock present powertrain control module PCM can not reduce engine knock by retarding timing 54 Powertrain Control Module PCM computer circuit problem analog to digital A D converter error OR Information Flag 5 volt reference ground flag will set if manifold absolute pressure MAP sensor signal handwheel sensor signal throttle position sensor
24. WOT Wide Open Throttle The vehicle operating condition brought about when the throttle is completely or nearly so open The ECM will typically deliver extra fuel to the engine at this time for acceleration purposes The ECM uses the Throttle Position Sensor to identify the WOT condition ABS BASICS A General Description of ABS Systems The following is an overview of Anti Lock Brake Systems ABS There are several different types and versions Refer to vehicle service manual for specific details IMPORTANT To service ABS systems safely and effectively you must obtain a service manual for your vehicle and carefully follow all procedures What is ABS ABS is a safety feature designed to minimize accidents during braking When engaged ABS stops the vehicle in the shortest distance possible while giving the driver the greatest amount of steering control Heavy braking on non ABS vehicles often causes wheels to lock up This leads to a wheel skid condition resulting in loss of maneuverability and a long stopping distance The job of ABS is to prevent wheel lock up Front Wheel Speed Sensors Master Cylinder The ABS System An ABS system combines a conven tional hydraulic braking system along with additional components including An ABS computer separate from the engine computer Wheel speed sensors Hydraulic control unit The computer module controls the ABS system This module is cal
25. a flash e EXAMPLES Code 12 looks like als lp gt AE Ses FLASH 3 second pause FLASH FLASH then light stays on FLASH 1 FLASH FLASH 2 Put 1 and 2 together code 12 Code 23 looks like lp gt lp al al ATA MAS SS FLASH FLASH 3 second pause FLASH FLASH FLASH then light stays on 10 Get More Codes if any from Flashing Anti Lock Light e Do this step after first code has been flashed and anti lock light is ON steadily e Do NOT turn ignition switch off Remove Code Scanner from test connector Then Re install Code mer into test connector The nextABS trouble code if any will be flashed in the same manner as the first code Repeat this step until all trouble codes have been read The ABS computer can store up to 7 trouble codes 11 Turn Ignition Key OFF 12 Remove Code Scanner and Re install Connector Cover if supplied The computer system is now back to normal operation 13 Refer to ABS Code Meanings on page 84 Teves Mark Il Version B This completes the code reading procedure At this point you can either e Have your vehicle professionally serviced Trouble codes indicate problems found by the computer or e Repair the vehicle yourself using trouble codes to help pinpoint the problem IMPORTANT Always follow vehicle service manual proce dures for any ABS repairs Erasing ABS Codes from Compute
26. be cleared until they have been read Refer to READING ABS CODES page 77 2 Drive the vehicle at a speed of greater than 18 MPH Trouble codes should automatically clear ABS Code Meanings Teves Mark II Version A IMPORTANT Always follow vehicle service manual procedures for any ABS repairs 11 EBCM Electronic Brake Control Module Failure In most cases this code indicates an EBCM failure Follow the appropriate chart to check the ground circuit 12 EBCM Electronic Brake Control Module Failure In most cases this code indicates an EBCM failure Follow the appropriate chart to check the ground circuit 21 Main Valve Checks for open shorted or intermittent condition in the main valve solenoid and its circuitry 22 Left Front Inlet Valve Checks for open shorted or intermittent condition in the left front inlet valve solenoid and its circuitry 23 Left Front Outlet Valve Checks for open shorted or intermittent condition in the left front outlet valve solenoid and its circuitry 24 Right Front Inlet Valve Checks for open shorted or intermittent condition in the right front inlet valve solenoid and its circuitry 25 Right Front Outlet Valve Checks for open shorted or intermittent condition in the right front outlet valve solenoid and its circuitry 26 Rear Inlet Valve Checks for open shorted or intermittent condition in the rear inlet valve solenoid and its circuitr
27. command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 72 which has the same meaning 53 Right Rear Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 73 which has the same meaning 54 Left Rear Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 74 which has the same meaning 61 Shorted Low Fluid or Hydraulic Pressure Switch or shorted ABS diode or associated circuitry This code will set if the low fluid switch the hydraulic pressure switch or the ABS diode or any of the associated circuitry exhibits a short circuit condition 71 Left Front Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 51 which has the same meaning 85 72 Right Front Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pr
28. connector the Assembly Line Diagnostic Link ALDL connector It may also be called the Assembly Line Communi cation Link ALCL or simply test connector e The connector is located under the dashboard on the driver s side e The connector may be in full view or it may be recessed behind a panel opening The connector may have a slip on cover labeled Diagnostic Connector Remove cover for testing Replace cover after testing Some vehicles require this cover in place for proper operation 4 Verify Ignition Key is OFF SESS SSS AAN E Cum TEST EN SE d 6 Plug the Code Scanner into the Test Connector e The Code 5 8 Scanner only fits ONE WAY into the test connector e The Code Scanner will not harm the vehicle computer Note The Code Scanner does not use all of the test connector contacts This is normal 7 Turn Ignition Key to ON Position but DO NOT START THE ENGINE WARNING Stay away from the radiator cooling fan It may turn on 8 Get Codes from the Flashing Anti Lock Light e Count flashes to get trouble codes Flashes begin after a few seconds Code 12 looks like ale ale als Av PAUSE WOW FLASH pause FLASH FLASH FLASH 1 FLASH FLASH 2 Put 1 and 2 together code 12 Code 23 looks like lp al xl Yr cl AN AL PAUSE TOTS IN FLASH FLASH pause FLASH FLASH FLASH e After all codes are sent the
29. connector for about 1 second then reinstall the Code Scanner for about one second Repeat this procedure 3 times within 10 seconds Leave the Code Scanner inserted in the connector the 3rd time ON gt e 1991 Corvette When the anti lock lamp begins to flash codes remove the Code Scanner from the connector for about 1 second then reinstall the Code Scanner for about 1 second Repeat this procedure 4 times within 10 seconds Leave the Code Scanner inserted in the connector the 4th time 56 3 Wait 15 seconds then observe the anti lock indicator lamp Code 12 the diagnostic system operational code should flash indicating that all trouble codes have been erased from memory Turn the ignition switch to the OFF position Remove the Code Scanner and reinstall the test connector cover if used on vehicle ABS Code Meanings Bosch 2S IMPORTANT Always follow vehicle service manual procedures for any ABS repairs 12 Diagnostic System Operational 21 Right Front Wheel Speed Sensor circuit Checks for open shorted or intermittent condition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 22 Right Front Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 25 Left Front Wheel Spe
30. cylinder Refer to vehicle service manual for specifications COYWRESSION TESTER Exhaust backpressure Check for any restrictions in the exhaust system Ignition timing If adjustable Verify timing is within specification Refer to vehicle service manual or Vehicle Emission Control Information VECI decal located in the engine compartment Be sure to disable computer spark advance timing circuit if used when checking basic timing Air induction system Check for intake manifold vacuum leaks Check for P carbon or varnish build up on throttle valve or idle speed control device 3 Read Codes Refer to Section 3 Reading Codes Remember there are two types of codes 13 Hard codes codes for problems which are present now Intermittent codes codes for problems which happened in the past but are not happening now Remember Check Engine light ON You have at least one hard code stored in memory You may have more hard or intermittent codes stored also Check Engine light OFF Stored codes are for intermittent problems Exception sometimes there are minor hard faults which do not turn on the Check Engine light How to Tell Hard Codes from Intermittent Codes Do the following if you are not sure e Write down all codes except code 12 For ex
31. few times to verify the code e Code flashing continues until the ignition key is turned OFF or the Code Scanner is unplugged 8 Turn Ignition Key OFF 9 Remove Code Scanner and Re install Connec tor Cover if supplied The computer system is now back to normal operation 10 Refer to ABS Code Meanings on page 89 Kelsey Hayes RWAL This completes the code reading procedure At this point you can either e Have your vehicle professionally serviced Trouble codes indicate problems found by the computer OF e Repair the vehicle yourself using trouble codes to help pinpoint the problem IMPORTANT Always follow vehicle service manual proce dures for any ABS repairs NOTE multiple trouble code storage This ABS system is only capable of displaying one code at a time Repair the failure which generated the displayed trouble code and then repeat the READING ABS CODES procedure to see if any more codes are stored Continue repeating the procedure until all codes are displayed diagnosed and repaired Erasing ABS Codes from Computer Memory Kelsey Hayes RWAL Erase codes from memory when you complete all repairs or to see if a problem will occur again Proceed as follows 1 Turn the ignition key to the OFF position 2 Remove the indicated fuse from the fuse block and wait at least 10 seconds e 1988 93 C amp K Trucks Remove the STOP HAZ fuse e 1989 92 Astro Safari
32. flashes both engine codes and transmis sion codes e Saturn Vehicles The Check Engine light flashes engine codes The Shift to D2 light flashes transmission codes Look for a code 11 flashed on the Check Engine light This is a signal telling you transmission codes will then be flashed on the Shift to D2 light Transmission codes are flashed in a way similar to engine codes 9 Turn Ignition Key OFF 10 Remove Code Scanner and Re install Connector Cover if supplied The computer system is now back to normal operation 11 Refer to Test Results chart on page 11 This completes the code reading procedure At this point you can either e Have your vehicle professionally serviced Trouble codes indicate problems found by the computer or e Repair the vehicle yourself using trouble codes to help pinpoint the problem 10 TEST RESULTS COMMENTS No indication on You have a problem which needs repair ira Engine before using the Code Scanner 9 Refer to Diagnostic Circuit Check chart r i i i in vehicle service manual Did not receive Code 12 Code 12 only Computer did NOT find a problem If a driveability problem persists perform Visual Inspection and Basic Mechanical Checks Section 4 Using Codes Refer to Diagnosis by Symptom charts in vehicle service manual Additional electrical and mechanical checks are listed Re
33. for lower emissions and better fuel economy This all began in the early 1980 s when purely mechani cal control systems just were not good enough anymore A computer could be programmed to precisely control the engine under various operating conditions and eliminate some mechanical parts making the engine more reliable Note that vehicle service manuals refer to the computer as either the ECM Engine Control Module or PCM Powertrain Control Module What the computer controls The main control areas of the computer are e Fuel delivery e Idle speed e Spark advance timing e Emission devices EGR valve carbon cannister etc The changes made to the basic engine to allow a computer to control these tasks are the only differences between an older engine and a computerized one A little later we will discuss just how the computer handles these tasks What has NOT changed A computer controlled engine is basically the same as earlier types It is still an internal combustion engine with pistons spark plugs valves and cams The ignition charging starting and exhaust systems are almost the same as well You test and repair these systems the same way as before using familiar tools The instruction manuals for these tools show you how to perform the tests Your compression gauge vacuum pump dwell tach meter engine analyzer timing light etc are still valuable The Engine Computer Control The computer mo
34. injector or incorrect fuel pressure can change the amount of fuel delivered and the computer would not know it The computer system is forced to operate open loop because no sensor type is available which can measure air fuel ratios when the engine is cold Hot engine cruise condition An example of Closed Loop operation The computer watches the coolant temperature and throttle position sensors to tell when the engine is all warmed up and cruising As before the computer determines the amount of air coming into the engine then delivers the amount of fuel that should provide the optimum air fuel mixture The big difference is that this time the computer uses the oxygen sensor to check how well its doing and re adjust things if needed to make sure the fuel delivery is correct For example If the oxygen sensor indicates a rich condition the computer will compen sate by reducing fuel delivery until the oxygen sensor signals an optimum air fuel ratio Likewise the computer will compensate for a lean condition by adding fuel until the oxygen sensor once again signals an optimum air fuel mixture This is an example of Closed Loop operation The control system performs an action expecting a certain result then checks the results and corrects its actions if necessary until the desired results are achieved The oxygen sensor only works when it is very hot During cold engine warm up a
35. lamp is ON and the brake warning lamp is OFF proceed to READING ABS CODES page 82 If the anti lock lamp is OFF and the brake warning lamp is ON refer to the proper diagnostic chart in the vehicle service manual If the anti lock lamp is ON and the brake warning lamp is ON refer to the proper diagnostic chart in the vehicle service manual If the anti lock lamp is OFF and the brake warning lamp is OFF then this indicates normal system operation or an intermittent problem Intermittent trouble codes may or may not be stored Reading ABS Codes Teves Mark Version B IMPORTANT Perform all steps in PRE DIAGNOSTIC VISUAL INSPEC TION and FUNCTIONAL CHECK before reading ABS codes 1 Safety First e Set the parking brake e Put shift lever in PARK automatic transmission or NEUTRAL manual transmission e Block the drive wheels e Make sure ignition key is in OFF position 2 Verify Codes are Stored e Turn the ignition key to the ON position but do not start the engine e Wait 30 seconds Seaman E AA e Observe anti lock 8 on TABS Light ON Codes are stored Proceed with testing Light OFF No codes are stored Stop testing e Turn ignition key OFF 3 Have a Pencil and Paper Ready This is for writing down all the codes 4 Find the Computer Test Connector e Service manuals call this connector the Assembly Line Diagnostic Link ALDL connector It may also be cal
36. loose dirty or corroded connection Check the connections at the wheel speed sensor connector the wheel speed sensor harness and the EHCU Electro Hydraulic Control Unit There may also be a problem in the wheel speed sensor or its associated tone toothed wheel Check for the proper air gap between the wheel speed sensor and tone wheel missing or broken teeth on the tone wheel a loose improperly mounted or mis adjusted wheel speed sensor 28 One or Two Wheel Speed Sensor Voltage Output Signals are erratic Trouble codes 23 27 33 or 37 may be set along with code 28 If one or more of these 4 codes are present use that code s to diagnose the failure If trouble code 28 is the only code set it is advisable to drive the vehicle an additional period of time until one of the 4 listed codes does set and then use that code chart for diagnosis lf code 28 persists as the only trouble code it indicates that an intermittent connection exists somewhere in the system All connections will have to be checked 29 All Wheel Speed Sensor Voltage Output Signals are erratic Trouble code 29 is usually caused by an improperly seated 8 way connector at the EHCU Electro Hydraulic Control Unit Check for corrosion or dirty contacts and that the connector is properly installed in the EHCU 31 Right Rear Wheel Speed Sensor Circuit resistance is incorrect This code is indicative of high resistance in this p
37. motor spindle See ISC definition During idle the throttle rests against the ISC spindle and activates the switch The ECM uses this switch signal to identify closed throttle condition then operates the engine in an idle or deceleration mode Inputs Electrical signals running into the ECM These signals come from sensors switches or other electronic modules They give the ECM information about vehicle operation ISC Idle Speed Control This refers to a small electric motor mounted on the throttle body and controlled by the ECM The ISC motor moves a spindle back and forth When the throttle is released during idle it rests on this spindle The ECM can control idle speed by adjusting this spindle position The ECM determines the desired idle speed by looking at battery voltage coolant temperature engine load and RPM Knock sensor This sensor is used to detect engine detonation Knocking When spark knock occurs the sensor sends a pulsing signal Depending upon vehicle this signal goes either to the ECM or a separate ESC Electronic Spark Control module Then the spark advance is retarded to eliminate detonation The sensor contains a piezoelectric element and is threaded into the engine block Vibrating the element generates the signal Special construction makes the element only sensitive to the engine vibrations associated with knocking MAF Mass Air Flow sensor This sen
38. of the spring accumulator hydraulic pressure is about 150 PSI The electric pump operates to remove fluid from the accumulators and return it to the master cylinder Some systems have no pump The spring driven diaphragm in the accumulator pushes brake fluid back into the master cylinder through a compensation port e High Pressure type Accumulator and pump used for both ABS and normal brake operation Accumulator stores fluid under very high pressure up to 2600 PSI The accumulator contains a moveable diaphragm which separates the inside into two chambers One chamber holds the hydraulic fluid The other side is filled with high pressure Nitrogen gas The gas acts as a very strong spring keeping the hydraulic fluid under great pressure The pressurized fluid is used during normal and ABS braking The electric pump is a special high pressure hydraulic type It runs as needed to maintain high hydraulic pressure in the accumulator The pump is not controlled by the ABS computer A pressure activated switch threaded into the accumulator fitting turns the pump on and off as required Warning Light All vehicles have a red BRAKE light on the dashboard to warn of problems in the normal braking system Some ABS systems use this BRAKE light to warn of ABS problems as well Other vehicles have a separate amber ANTILOCK dashboard light to warn of ABS problems The ABS computer controls
39. on e If the light does not turn on you have a problem with this circuit which must be repaired before proceeding Refer to the Diagnos tic Circuit Check procedure in your vehicle service manual e Turn ignition key OFF 3 Have a Pencil and Paper Ready This is for writing down all the codes 4 Find the Computer Test Connector e Service manuals call this connec tor the Assembly Line Diagnostic Link ALDL connector It may also be called the Assembly Line Communication Link ALCL or simply test connector e The connecter is located under the dashboard on the driver s side Exceptions LeMans Located behind passen ger side kick panel Remove snap on cover for access Fiero Located in the center console behind cover panel Corvette Sometimes located in centerconsole behind ashtray Consult service manual for exact location e The connector may be in full view or it may be recessed behind a panel An opening in the panel allows access to recessed connectors e The connector may have a slip on cover labeled Diagnostic Connector Remove cover for testing Replace cover after testing Some vehicles require this cover in place for proper operation 5 Verify Ignition Key is OFF O lt gt 6 Plug the Code Scanner into the Test Connector Put TEST switch on ENGINE e The Code Scanner only fits ONE WAY into the test connector e The Code
40. on 8 Get Codes from the Flashing Anti Lock Light e Count flashes to get trouble codes Flashes begin after a few seconds Code 12 looks like ale ale als Av PAUSE ZETA FLASH pause FLASH FLASH FLASH 1 FLASH FLASH 2 Put 1 and 2 together code 12 Code 23 looks like NIN NUNN AN AN PAUSE HOTS IN FLASH FLASH pause FLASH FLASH FLASH e Each code is flashed three 3 times before the next trouble code is sent e After all codes are sent the whole sequence is repeated This continues until the ignition key is turned OFF so you can double check your code list Example of code 12 only aly NYEN Av PAUSE CR FLASH pause FLASH FLASH longer pause aly NIN Av PAUSE SITAS FLASH pause FLASH FLASH longer pause OC PAUSE THESE FLASH pause FLASH FLASH even longer pause then start over again Example of code series 12 and 24 al NTEN y Av PAUSE SITAS FLASH pause FLASH FLASH longer pause aly NUNS Av PAUSE Oa FLASH pause FLASH FLASH longer pause al NTEN Av PAUSE WII FLASH pause FLASH FLASH even longer pause then go to next code D SE als als als ale AN AN PAUSE TOTS AN AN FLASH FLASH pause FLASH FLASH FLASH FLASH longer pause D SE NUNN AE AN AN PAUSE CR E AN FLASH FLASH pause FLASH FLASH FLASH FLASH longer pause D SE als als als ale AN AN PAUSE TOTO AN AN FLASH F
41. read computer trouble codes if e The Check Engine light comes ON when the engine is RUNNING Or e Vehicle engine is running poorly and Check Engine light is OFF The Check Engine light The engine computer turns the Check Engine light on and off as needed This dashboard message light is either amber or red and labeled Check Engine or Service Engine Soon or Service Engine Now or marked with a small engine picture Check Engine light Normal Operation The Check Engine light is normally OFF when the engine is RUNNING NOTE The light will come on when ignition key is in ON position but the engine is OFF For example before you start the engine This is a normal test of all the dashboard message lights If the Check Engine light does not come on you have an electrical problem which needs repair Refer to the Diagnostic Circuit Check steps in the Basic Diagnostic Procedures section of your vehicle service manual Check Engine Light Problem Spotted Light ON and stays ON when the engine is RUNNING The computer sees a problem that does not go away A hard failure The light will stay on as long as the problem is present A trouble code is stored in computer memory A hard code Use the Code Scanner at the earliest convenient time to obtain codes Refer to se
42. referred to as outputs Devices called actuators are powered by the computer to control things Actuator types include e Solenoids These are used to control a vacuum signal bleed air control fuel flow etc e Relays These switch high amperage power devices on and off such as electric fuel pumps or electric cooling fans e Motors Small motors are often used to control idle speed Other output signals Not all of the computer outgoing signals go to actuators Sometimes information is sent to electronic modules such as ignition or trip computer How the computer controls fuel delivery Good performance and low emissions depend upon precise fuel control Early computer controlled vehicles used electronically adjustable carburetors but fuel injectors were soon introduced The job of the computer is to provide the optimum mixture of air and fuel air fuel ratio to the engine for best performance under all operating conditions The computer needs to know e what the engine operating condition is Sensors used coolant temperature throttle position manifold absolute pressure mass air flow RPM NOw much air is coming into the engine Sensors used mass air flow or a combination of manifold absolute pressure manifold air temperature RPM how much fuel is being delivered The computer knows this by how long it turns on the fuel injectors The computer uses a feedback c
43. signal to the computer and generate more trouble codes Code lists This page Codes from flashing Check Engine light e GM engine codes e GM electronic transmission codes e Saturn engine codes Page 21 Codes from flashing Shift to D2 light e Saturn electronic transmission codes Refer to Section 4 Using Codes for troubleshooting tips and steps to erase codes from computer memory GM Saturn Engine Codes GM Transmission Codes Saturn transmission code list begins on page 21 11 Transaxle codes present Saturn Whenever code 11 is sent it means transmission codes will be flashed next on the Shift to D2 light Refer to page 19 for Saturn transmission code list 12 Diagnostic test is working properly Engine computer verifies no RPM Reference Pulses are present during engine off testing 13 Oxygen 02 sensor signal stays low lean during warm engine cruise or sensor circuit is open or left sensor circuit is open dual sensor models 14 Coolant temperature sensor CTS signal voltage is low 15 Coolant temperature sensor CTS signal voltage is high 16 Battery or alternator problem voltage too high or low OR Direct ignition system DIS fault line open or shorted to ground OR Ignition system fault Loss of 2X or Low Resolution Pulse signal OR Transmission speed error 16 17 RPM signal problem OR Cams
44. starts If is does not check the brake warning lamp circuit in accordance with the vehicle service manual instructions 2 Turn the engine OFF Turn the ignition key to the ON RUN position but do not start the engine The anti lock lamp should illuminate for about 4 seconds and then turn OFF if no trouble codes are currently stored However history trouble codes may be stored Proceed to Step 3 below If the anti lock lamp stays ON trouble codes are stored Proceed directly to READING ABS CODES page 66 3 Drive the vehicle at least 20 MPH If the anti lock lamp turns ON proceed to READING ABS CODES page 66 Reading ABS Codes Bosch 2U Version B IMPORTANT Perform all steps in PRE DIAGNOSTIC VISUAL INSPEC TION and FUNCTIONAL CHECK before reading ABS codes 1 Take Safety Precautions e Set parking brake block drive wheels e Put shift lever in PARK automatic transmission or NEUTRAL manual transmission e Make sure ignition key is in OFF position 2 Have a Pencil and Paper Ready This is for writing down all the codes 3 Find the Computer Test Connector e Service manuals call this connector the Assembly Line Diagnostic Link ALDL connector It may also be called the Assembly Line Commu nication Link ALCL or simply test connector e The connector is located under the dashboard on the driver s side e The connector may be in full view or it may be recessed behind a pa
45. the associated wiring can also set this code 23 Right Front Wheel Speed Sensor Voltage Output is erratic Erratic voltage output usually indicates a loose dirty or corroded connection Check the connections at the wheel speed sensor connector the wheel speed sensor harness and the EHCU Electro Hydraulic Control Unit There may also be a problem in the wheel speed sensor or its associated tone toothed wheel Check for the proper air gap between the wheel speed sensor and tone wheel missing or broken teeth on the tone wheel a loose improperly mounted or mis adjusted wheel speed sensor 25 Left Front Wheel Speed Sensor Circuit resistance is incorrect This code is indicative of high resistance in this particular wheel speed sensor circuit The resistance of the wheel speed sensor may 93 be out of specification or there may be loose corroded or dirty connections in this circuit 26 Left Front Wheel Speed Sensor Voltage Output is incorrect This code indicates a problem in the wheel speed sensor or its associated tone toothed wheel Check for the proper air gap between the wheel speed sensor and tone wheel missing or broken teeth on the tone wheel a loose improperly mounted or mis adjusted wheel speed sensor An intermittent connection in the associated wiring can also set this code 27 Left Front Wheel Speed Sensor Voltage Output is erratic Erratic voltage output usually indicates a
46. the positive junction block e 1992 Brougham Check the GA TRANS fuse in the underdash fuse block Check the ABS fuse in the underdash fuse block Check the rust colored fusible link E on the positive junction block 3 Check that the over voltage relay ABS 6 way connector and EBCM Electronic Brake Control Module connectors are properly installed not loose 4 Check that the parking brake switch is functioning properly This completes the visual inspection Perform FUNCTIONAL CHECK before reading codes Functional Check Brougham 1 Start the engine The brake warning lamp should come ON during engine cranking and turn OFF shortly after the engine starts If it does not check the brake warning lamp circuit in accordance with vehicle service manual instructions 2 Turn the engine OFF Turn the ignition key to the ON RUN position but do not start the engine The anti lock lamp should illuminate for about 4 seconds and then turn OFF if no trouble codes are currently stored However history trouble codes may be stored Proceed directly to Step 3 below If the anti lock lamp stays ON trouble codes are stored Proceed directly to READING ABS CODES 3 Drive the vehicle at least 20 MPH If the anti lock lamp turns ON proceed to READING ABS CODES Caprice Custom Cruiser Roadmaster 1 Start the engine The brake warning lamp should come ON during engine cranking and turn OFF shortly
47. voltage signal to the ABS computer The computer uses this signal to modify ABS control of the rear brakes How ABS Controls Brakes Depending upon system the ABS computer will either continuously monitor wheel speed Or wait for brake pedal application before monitoring wheel speed The ABS computer controls braking action when wheel speed acceleration or deceleration indicates lock up is about to occur Four Wheel Drive Vehicle Note The ABS computer will not allow ABS braking during four wheel drive operation A switch in the four wheel drive powertrain sends a signal to the ABS computer The ABS computer controls brake line pressure by operating one or more solenoid valves in the Hydraulic Control Modulator Some systems use two solenoid valves per brake circuit an isolation valve and a dump valve Other systems use a special two stage solenoid per brake circuit Either system controls brake line pressure in the same way Normal Braking no ABS action ABS computer sees normal wheel speed changes No ABS action is necessary From Isolation JJ Master Valve Pf Cylinder OPEN To Wheel Caliper or Cylinder Dump Valve CLOSED Accumulator or Reservoir HYDRAULIC PRESSURE FLOW Isolation valve is OPEN not energized Brake circuit operates normally Hydraulic pressure from master cylinder passes through isolation valve to wheel caliper cylinder
48. 18 in the underdash fuse block Check the black M and blue U colored fusible links on the positive junction block e 1992 Eldorado Seville Check the A1 fuse in the trunk compartment fuse block Check fuse number 5 in the RIGHT MAXI fuse block Check fuse number 6 in the RIGHT MAXI fuse block e 1992 Riviera Check fuse number 4 in the interior relay center Check the black and blue colored fusible links on the positive junction block 64 e 1992 Toronado Trofeo Check fuse number 18 in the underdash fuse block Check the black and blue colored fusible links on the positive junction block e 1993 Riviera Check fuse number 4 in the interior relay center Check fuse number 6 and 9 in the underdash fuse block Check the black colored M and P fusible links on the positive junction block 3 Check that all ABS TCS connec tors and EBCTM Electronic Brake and Traction Control Module connectors are properly installed not loose 4 Check that the parking brake switch is functioning properly 5 Check that the brake pressure modulator valve ground stud is clean and tight 6 Check the over voltage protection relay and its connector This completes the visual inspection Perform FUNCTIONAL CHECK before reading codes Functional Check 1 Startthe engine The brake warning lamp should come ON during engine cranking and turn OFF shortly after the engine
49. 4 ale ale als Av PAUSE IA FLASH pause FLASH FLASH longer pause al als G PAUSE AV FLASH pause FLASH FLASH longer pause ale ale ale Av PAUSE SIA FLASH pause FLASH FLASH even longer pause then go to next code E a ale ale als ale ale AS ALE SAS NS FLASH FLASH pause FLASH FLASH FLASH FLASH longer pause E A als als als ale ale SOs ALE SS NS FLASH FLASH pause FLASH FLASH FLASH FLASH longer pause E A als ale als ale ale EE FLASH FLASH pause FLASH FLASH FLASH FLASH even longer pause then start all over from the very beginning e A code 12 is always sent even when the computer sees no problem This tells you the computer diagnostic checks are working properly If you do not get a code 12 or if the Check Engine light does not flash you have a problem which must be repaired Refer to Diagnostic Circuit Check procedure in vehicle service manual e All codes are two 2 digits long e Codes are sent in numeric order from the lowest number to the highest Transmission Codes The engine computer can send trouble codes for transmission problems if the vehicle has a computer controlled transmission NOTE Some diesel powered trucks have a computer controlled transmis sion These vehicles will only send transmission related codes since the the diesel itself is not computer controlled e GM Vehicles The Check Engine light
50. 5 Left Front Solenoid Valve circuit This code will set if the physical position of the subject valve does not match the commanded position as given by the EBCM Electronic Brake Control Module 55 Rear Axle Solenoid Valve circuit This code will set if the physical position of the subject valve does not match the commanded position as given by the EBCM Electronic Brake Control Module 63 61 Pump Motor or Motor Relay circuit This code will set if the position of the motor relay contacts do not match the commanded position of those contacts as given by the EBCM Electronic Brake Control Module There is a motor monitoring circuit in the EBCM which will detect a defective relay or pump motor 63 Solenoid Valve Relay circuit This code will set if the position of the valve relay contacts do not match the commanded position of those contacts as given by the EBCM Electronic Brake Control Module There is a motor monitoring circuit in the EBCM which will detect a defective relay or a failure in the associated circuitry 71 EBCM Electronic Brake Control Module failure This code will set if there is an internal failure of the Electronic Brake Control Module SYSTEM 3 Bosch 2U Version B 1991 Brougham Eldorado Reatta Riviera Seville Toronado Trofeo 1992 Eldorado Riviera Seville Toronado Trofeo 1993 Riviera Pre Diagnostic Visual Inspection Complete all steps before reading t
51. 90 90 Model Astro Blazer Bravada C Series Pickup Truck DeVille Eldorado G Series Van Jimmy K Series Pickup Truck S Series Pickup Truck Safari Seville Sierra Sonoma Suburban T Series Pickup Truck Yukon NOTE Two different ABS systems were available for this vehicle Each system has a different code reading procedure Do the following to identify System Page 8 90 7 or 8 See note below 8 90 7 or 8 See note below 4 70 4 70 8 90 8 90 7 or 8 See note below 7 or 8 See note below 8 90 4 70 8 90 8 90 8 90 7 or 8 See note below 8 90 which system is installed e Examine the Electro Hydraulic Control Unit EHCU This assembly has both electrical and hydraulic connections It is installed between the master cylinder and the wheel caliper or cylinder If there are 5 hydraulic connections 2 inlet 3 outlet then vehicle has System 8 Go to page 90 Less than 5 hydraulic connections means vehicle has System 7 Go to page 86 52 SYSTEM 1 Bosch 2S 1990 Corvette 1991 Corvette Pre Diagnostic Visual Inspection Complete all steps before reading trouble codes 1 Check that all ABS system grounds are clean and tight 2 Check power sources which supply various parts of ABS system e 1990 1991 Corvette Check the AIR BAG fuse in the underdash fuse block Check the BRAKE fuse in the underdash fuse block Check the STOP HAZ fuse in the
52. 90 Bonneville SSE 97 ONE 1 YEAR LIMITED WARRANTY Bosch warrants to the original purchaser that this product will be free from defects in materials and workmanship for a period of one 1 year from the date of original purchase Any unit that fails within this period will be replaced or repaired at Bosch s discretion without charge If you need to return product please follow the instructions below This warranty does not apply to damages intentional or accidental alterations or improper or unreasonable use DISCLAIMER OF WARRANTY BOSCH DISCLAIMS ALL EXPRESS WARRANTIES EXCEPT THOSE THAT APPEAR ABOVE FURTHER BOSCH DISCLAIMS ANY IMPLIED WARRANTY OF MERCHANT ABILITY OF THE GOODS OR FITNESS OF THE GOODS FOR ANY PURPOSE TO THE EXTENT ALLOWED BY LAW ANY IMPLIED WARRANTY OF MERCHANTABILITY OR OF FITNESS APPLICABLE TO ANY PRODUCT IS SUBJECT TO ALL THE TERMS AND CON DITIONS OF THIS LIMITED WARRANTY SOME STATES DO NOT ALLOW LIMITATIONS ON HOW LONG AN IMPLIED WARRANTY LASTS SO THIS LIMITATION MAY NOT APPLY TO A SPECIFIC BUYER LIMITATION OF REMEDIES IN NO CASE SHALL BOSCH BE LIABLE FOR ANY SPECIAL INCIDENTAL OR CONSE QUENTIAL DAMAGES BASED UPON ANY LEGAL THEORY INCLUDING BUT NOT LIM ITED TO DAMAGES FOR LOST PROFITS AND OR INJURY TO PROPERTY SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF INCIDENTAL OR CON SEQUENTIAL DAMAGES SO THIS LIMITATION OR EXCLUSION MAY NOT APPLY TOA SPECIFIC BUYER THIS WARRANTY GIVES
53. 990 Brougham 1991 Caprice Custom Cruiser Roadmaster 1992 Brougham Pre Diagnostic Visual Inspection Complete all steps before reading trouble codes 1 Check that all ABS system grounds are clean and tight e 1990 Brougham Check the ground that is located on the right front corner of the right fender Check the ground that is located near the cruise control servo on the fender e 1991 Caprice Custom Cruiser Roadmaster Check the 2 grounds that are located near the left headlight One is on the headlight support in front of the vapor canister the other is close to the wiring harness Check the ground that is located near the center of the left rear quarter panel Check the ground that is located near the thermostat housing e 1992 Brougham Check the ground that is located on the right front corner of the right fender Check the ground that is located near the cruise control servo on the fender 2 Check power sources which supply various parts of ABS system e 1990 Brougham Check the GA TRANS fuse in the underdash fuse block Check the ABS fuse in the underdash fuse block Check the STOP HAZ fuse in the underdash fuse block Check the rust colored fusible links on the positive junction block e 1991 Caprice Custom Cruiser Roadmaster Check fuse number 3 17 and 19 in the main fuse block Check the rust colored fusible link D on
54. ABS system is a higher perfor mance version of the RWAL version just described Used on rear wheel drive vehicles this system delivers short stopping distance and maneuver ing control during heavy braking All four wheels are ABS controlled Three hydraulic braking channels are used right front wheel left front wheel and a single channel for both rear wheels The ABS computer uses a three channel Hydraulic Control Modulator described later to operate the individual brake circuits as necessary The two rear wheels are monitored with a single speed sensor usually mounted in the differential This is similar to the RWAL system described before Two more speed sensors individually monitor each of the front two wheels e AWAL 4 Wheel Anti Lock also called 4 Channel This ABS system is similar to the 3 channel version previously described but is designed for front wheel drive vehicles The main difference is that four speed sensors are used instead of three to individually monitor all four wheels The hydraulic portion is the same as the 3 Channel system The ABS computer uses a three channel Hydraulic Control Modulator to control the right front wheel the left front wheel and both rear wheels ABS Components Electronic Brake Control Module EBCM May also be called Electronic Control Unit ECU or similar This is a computer module the brains of the ABS system The module is located either in
55. AUSE W FLASH pause FLASH FLASH longer pause ale ale als Av PAUSE WI FLASH pause FLASH FLASH even longer pause then start over again Example of code series 12 and 24 ale ale als Av PAUSE AV FLASH pause FLASH FLASH longer pause als NUN Av PAUSE WOT FLASH pause FLASH FLASH longer pause ale ale als Av PAUSE ZETA FLASH pause FLASH FLASH even longer pause then go to next code ale als NEN VINNY AN AN PAUSE TOTS IN AN FLASH FLASH pause FLASH FLASH FLASH FLASH longer pause lp als als als als ale AN AN PAUSE TOTS AN AN FLASH FLASH pause FLASH FLASH FLASH FLASH longer pause lp gt NUNN INS AN AN PAUSE ACACIA FLASH FLASH pause FLASH FLASH FLASH FLASH even longer pause then start all over from the very beginning e Acode 12 is always sent even when the computer sees no problem This tells you the computer diagnostic checks are working properly e All codes are two 2 digits long 9 Turn Ignition Key OFF 10 Remove Code Scanner and Re install Connector Cover if supplied The computer system is now back to normal operation 11 Refer to ABS Code Meanings on page 69 Bosch 2U Version B This completes the code reading procedure At this point you can either e Have your vehicle professionally serviced Trouble codes indicate problems found by the computer or e Repair the vehicle yourself usi
56. CM controls the spark advance timing A signal called EST goes from the ECM to the ignition module which fires the spark coil The ECM determines optimum spark timing from sensor information engine speed and RPM throttle position coolant temperature engine load vehicle speed Park Neutral switch position and knock sensor condition EVO Electronic Variable Orifice actuator This is a solenoid mounted in the power steering pump It is used in some variable assist power steering systems The solenoid controls the amount of fluid passed to the steering gear Increasing fluid flow generates more power steering assist The ECM controls the solenoid by using a duty cycle type signal see duty cycle definition The ECM uses information from the vehicle speed sensor VSS and the handwheel sensor which sends a signal related to the rate of steering wheel turning During low speed turns the ECM increases the EVO solenoid opening to provide additional steering assist The ECM decreases steering assist during straight line driving by reducing fluid flow through the EVO solenoid EVRV Electronic Vacuum Regulator Valve This actuator is controlled by the ECM and is used to vary the amount of vacuum applied to a vacuum operated device usually the EGR valve FBC Feedback Carburetor This is used on early versions of computer controlled engines It is a carburetor which can have its fuel delivery modif
57. CODE SCANNER Car Computer Code Reader Domestic GM amp Saturn CODE Se ANNER Car Computer Code Reader Lector de C digos de Computadoras de Autom vil GM y Saturn nacionales de EE UU con Systemas MCU y EEC IV para EUA Instrucci nes en espa ol p gina 99 Tensi n 14V Para Nombre Domicilio y Telefono Hecho en Ching Ge Importador Ver Empaque CODE SCANNER Congratulations on purchasing your Code Scanner for accessing engine trouble codes required for repairing vehicles equipped with computers You can have confidence this product maintains the highest quality in manufacturing and will provide you years of reliable service This instruction manual is divided into several key sections You will find detailed steps on using the Code Scanner and important information about trouble code meanings how a computer controls engine operation and more Identifying the problem is the first step in solving that problem Your Code Scanner can help you determine by accessing the engine computer trouble codes Armed with that knowledge you can either refer to an appropriate service manual or discuss your problem with a knowl edgeable service technician In either event you can save yourself a lot of valuable time and money in auto repair And feel confident that your vehicle s problem has been fixed CONTENTS Engine Transmission Section 1 About Codes oooccccccccccncccncncccnnnos 5 2 W
58. IAGNOSTIC VISUAL INSPEC TION and FUNCTIONAL CHECK before reading ABS codes 1 Take Safety Precautions e Set parking brake block drive wheels e Put shift lever in PARK automatic transmission or NEUTRAL manual transmission e Make sure ignition key is in OFF position 2 Have a Pencil and Paper Ready This is for writing down all the codes 3 Find the Computer Test Connec tor e Service manuals call this connector the Assembly Line Diagnostic Link ALDL connector It may also be called the Assembly Line Commu nication Link ALCL or simply test connector e The connecter is located under the dashboard on the driver s side e The connector may be in full view or it may be recessed behind a panel opening e The connector may have a slip on cover labeled Diagnostic Connector Remove cover for testing Replace cover after testing Some vehicles require this cover in place for proper operation 4 Verify Ignition Key is OFF ABS ENGINE Se e 5 Put the TEST switch on ABS 54 6 Plug the Code Scanner into the test connector Le e The Code Scanner only fits ONE WAY into the test connector e The Code Scanner will not harm the vehicle computer Note The Code Scanner does not use all of the test connector contacts This is normal 7 Turn Ignition Key to ON Position but DO NOT START THE ENGINE WARNING Stay away from the radiator cooling fan It may turn
59. LASH pause FLASH FLASH FLASH FLASH even longer pause then start all over from the very beginning e A code 12 is always sent even when the computer sees no problem This tells you the computer diagnostic checks are working properly e All codes are two 2 digits long 9 Turn Ignition Key OFF 10 Remove Code Scanner and Re install Connector Cover if supplied The computer system is now back to normal operation 11 Refer to ABS Code Meanings on page 57 Bosch 2S This completes the code reading procedure At this point you can either e Have your vehicle professionally serviced Trouble codes indicate problems found by the computer Or e Repair the vehicle yourself using trouble codes to help pinpoint the problem IMPORTANT Always follow vehicle service manual procedures for any ABS repairs Erasing ABS Codes from Computer Memory Bosch 2S Erase codes from memory whenever you complete a repair or to see if a problem will occur again Note The computer will automatically erase codes after several restarts typically 100 if the problem does not return Proceed as follows 1 Turn the ignition switch to the OFF position Plug the Code Scanner make sure the TEST switch is in the ABS position into the test connector 2 Turn the ignition switch to the ON position Then e 1990 Corvette When the anti lock lamp begins to flash codes remove the Code Scanner from the
60. TEST switch on ENGINE The engine gt computer is now a in the Field 25 Diagnostic Mode The flashing Check Engine light shows how the fuel control system is operating See below Read Section 7 Computer Basics or Section 8 Glossary for an explanation of Open Loop and Closed Loop operation IMPORTANT The oxygen sensor needs to be hot so the computer can check the signal for proper fuel delivery Warm the engine by idling for 2 minutes at 2000 RPM Then gently rev the engine from idle to part throttle several times This creates a changing sensor signal for the computer Finally keep the throttle steady or at idle for the rest of the test Light flashes 2 times a second The computer is in Open Loop operation The computer will run open loop if it does not see an oxygen sensor signal because The oxygen sensor is not hot enough to operate normal condition if engine too cold or sensor cooled down during idle or Open circuit problems exist bad sensor or wiring Note that this condition will generate a trouble code Light flashes once a second The computer is in Closed Loop operation The oxygen sensor is sending a signal e Light equally ON and OFF while flashing system is running correctly proper air fuel mixture e Light mostly ON while flashing system is running rich e Light mostly OFF while flashing system is run
61. The switches are activated by hydraulic pressure and may be normally open or closed depending upon vehicle The ECM uses gear information for control of the torque convertor clutch some emission systems and for transmission diagnostic purposes Ground The return path for current to flow back to its source Usually the negative battery terminal It is also the reference point from which voltage measure ments are made That is it is the connection place for the minus test lead from the voltmeter Hall Effect sensor This sensor is a three wire type containing electronic circuitry Two wires supply power and ground The third wire carries the sensor signal back to the ECM The sensor consists of a permanent magnet and a small module containing a transistorized Hall Effect switch A small air gap separates the sensor and the magnet The magnetic field causes the Hall switch to turn on and send out a low voltage signal If a metal strip iron or steel is placed in the gap it will block the magnetic field from reaching the Hall device This causes the Hall switch to turn off and send a high voltage signal out on the signal wire The metal strips blades are part of a cup or disk attached to a rotating component such as the crankshaft or camshaft As the blades pass through the sensor gap the signal voltage will switch high and low creating a series of pulses The ECM determines the speed of rotatio
62. YOU SPECIFIC LEGAL RIGHTS AND YOU MAY ALSO HAVE OTHER RIGHTS WHICH VARY FROM STATE TO STATE TO USE YOUR WARRANTY If you need to return the unit please follow this procedure 1 Call Bosch Technical Support at 1 800 228 7667 Our Technical Service Representatives are trained to assist you Proof of purchase is required for all warranty claims For this reason we ask that you retain your sales receipt In the event that product needs to be returned the Technical Service Rep resentative will provide you with the address where you can send the unit You will need to provide us with a contact name daytime phone number and a description of the problem If possible return the product in its original package with cables and acces sories Include your return address on the outside of the package and send the unit to the address provided by your Technical Service Representative You will be responsible for shipping charges in the event that your repair is not covered by warranty OUT OF WARRANTY REPAIR If you need product repaired after your warranty has expired please call Technical Support at 800 228 7667 All information illustrations and specifications contained in this manual are based on the latest information available from industry sources at the time of publication No warranty expressed or implied can be made for its accuracy or completeness nor is any responsibility assumed by Bosch or anyone connected with it for
63. a computer housed in a metal box with a number of sensors and actuators connected with a wiring harness lts job is to control fuel delivery idle speed spark advance timing and emission systems The ECM receives information from sensors then energizes various actuators to control the engine The ECM is sometimes called PCM Powertrain Control Module in vehicles having other computers These other computers are used for climate control entertainment systems etc EFI Electronic Fuel Injection A term applied to any system where a computer controls fuel delivery to an engine by using fuel injectors EGR Exhaust Gas Recirculation The EGR system recirculates exhaust gases back into the intake manifold to reduce NO emissions The EGR valve controls the flow of exhaust gases back into the intake manifold Some EGR valves are operated with a vacuum signal while others are electrically controlled The amount of EGR valve opening determines the flow through the valve EGR recirculation is only used during warm engine cruise conditions EGR flow at other times can cause stalling or no starts There are three types of EGR systems controlled by the ECM One system uses exhaust backpressure to operate the EGR valve The ECM does not control the EGR valve in this case but it can switch off the valve completely when desired The ECM operates a solenoid switch to cut off the backpressure control signal to the
64. a thermistor a resistor whose resistance decreases with increases in temperature The sensor is threaded into the engine block and contacts the engine coolant The ECM uses this signal for control of fuel delivery spark advance and EGR flow Digital Signal An electronic signal which has only two 2 voltage values a low value close to zero and a high value usually 5 volts or greater Sometimes the low voltage condition is called Off and the high voltage condition is called On Signals which can have any voltage value are called analog signals DIS Distributorless Ignition System or Direct Ignition System A system which produces the ignition spark without the use of a distributor Driver A transistor switch inside the ECM used to apply power to an external device This allows the ECM to control relays solenoids and small motors 34 Duty Cycle A term applied to frequency signals those which are constantly switching between a small voltage value close to zero and a larger value usually 5 volts or greater Duty cycle is the percentage of time the signal has a large voltage value For example if the signal is high large voltage half of the time then the duty cycle is 50 If the signal is high only one fourth of the time then the duty cycle is 25 A duty cycle of 0 means the signal is always at a low value and not changing A duty
65. aft Whenever a tooth from the ring passes by the sensor it attracts the magnetic field lines surrounding the magnet As the field lines move they pass through the wire coil and generate a small voltage pulse magnetic induction principle Thus a voltage pulse is generated every time a tooth passes by the sensor coil This voltage signal is sent to the ABS computer The ABS computer determines wheel speed by measuring how fast pulses appear The faster the wheel spins the more quickly pulses will appear Note The voltage pulses get larger as the wheel speeds up The computer ignores pulse size Values can range from a fraction of a volt low speed to several volts high speed Hydraulic Control Modulator This is an assembly containing solenoid operated hydraulic valves It Hydraulic Control Modulator Typical IS ON Typical Rear Sensor is usually mounted close to the master cylinder Some systems combine the hydraulic control modulator and the master cylinder into one complete unit The valves are connected in the brake lines between the master cylinder and the wheel caliper or wheel cylinder The ABS computer controls brake line pressure by operating one or more of these solenoid valves In ABS systems the process of varying brake pressure Is called modulation This is why the solenoid assembly is called a modulator Some modulator types use two solenoid valves per
66. after the engine starts If it does not check the brake warning lamp circuit in accordance with vehicle service manual instructions 2 Turn the engine OFF Turn the ignition key to the ON RUN position but do not start the engine The anti lock lamp should illuminate for about 2 seconds and then turn OFF if no trouble codes are currently stored however history trouble codes may be stored Proceed to Step 3 below If the anti lock lamp stays ON trouble codes are stored Proceed directly to READING ABS CODES If the anti lock lamp does not turn ON at all or flashes very briefly less than 1 2 of a second a problem exists in the anti lock lamp circuitry See your vehicle service manual 3 Drive the vehicle at least 20 MPH If the anti lock lamp turns ON proceed to READING ABS CODES 99 Reading ABS Codes Bosch 2U Version A IMPORTANT Perform all steps in PRE DIAGNOSTIC VISUAL INSPEC TION and FUNCTIONAL CHECK before reading ABS codes 1 Take Safety Precautions e Set parking brake block drive wheels e Put shift lever in PARK automatic transmission or NEUTRAL manual transmission e Make sure ignition key is in OFF position 2 Have a Pencil and Paper Ready This is for writing down all the codes 3 Find the Computer Test Connector e Service manuals call this connector the Assembly Line Diagnostic Link ALDL connector It may also be called the Assembly Line Commu nication Lin
67. ample 15 34 Erase codes from computer memory Refer to Step 5 Drive vehicle for at least 10 minutes at normal temperature cruise speed and load The computer may want to verify a fault for several minutes before storing a code Read codes again Codes which return are hard faults Codes which do not return are intermittent faults For example if you see code 15 but not 34 then you know code 15 is a hard code and code 34 was intermittent You troubleshoot the hard problems differently from the intermittent ones 4 Use Vehicle Service Manual Dealing with Hard Codes Refer to the vehicle service manual diagnostic code charts e Follow all the steps in the diagnostic procedure for the trouble code e Be sure to erase the trouble codes from computer memory after completing repair work See Step 5 Erasing Codes from Computer Memory e Drive vehicle for at least 10 minutes at normal temperature cruise speed and load Read codes again to verify trouble code is gone problem fixed Other codes may have been repaired at the same time Dealing with Intermittent Codes These codes are for problems which happened in the past but are not present now e Usually these problems are due to loose connections or bad wiring The problem cause can often be found with a thorough visual and hands on inspection Refer to Step 1 Visual Insp
68. anel An opening in the panel allows access to recessed connectors e The connector may have a slip on cover labeled Diagnostic Connector Remove cover for testing Replace cover after testing Some vehicles require this cover in place for proper operation 5 Verify Ignition Key is OFF e 6 Put TEST switch on ABS gt EK 7 Plug the Code Scanner into the test connector e The Code Scanner only fits ONE WAY into the test connector e The Code Scanner will not harm the vehicle engine computer Note The Code Scanner does not use all of the test connector contacts Also one Code Scanner pin may plug into an empty test connector position This is normal 8 Turn Ignition Key to ON Position but DO NOT START THE ENGINE WARNING Stay away from the radiator cooling fan It may turn on 9 Get a Trouble Code from Flashing Anti Lock Light e All codes are two 2 digits long e Count flashes to get trouble codes Flashes start aes after about a 4 D A H S second delay p p The first digit AA is flashed then there is a 3 second pause then the second digit is flashed then the anti lock light turns ON and stays ON Do not count this steady light as a flash e EXAMPLES Code 12 looks like AE al gt Av PAUSE oy FLASH 3 second pause FLASH FLASH then light stays on FLASH 1 FLASH FLASH 2 Put 1 and 2 together code 12
69. articular wheel speed sensor circuit The resistance of the wheel speed sensor may be out of specification or there may be loose corroded or dirty connections in this circuit 32 Right Rear Wheel Speed Sensor Voltage Output is incorrect This code indicates a problem in the wheel speed sensor or its associated tone toothed wheel Check for the proper air gap between the wheel speed sensor and tone wheel missing or broken teeth on the tone wheel a loose improperly mounted or mis adjusted wheel speed sensor An intermittent connection in the associated wiring can also set this code 33 Right Rear Wheel Speed Sensor Voltage Output is erratic Erratic voltage output usually indicates a loose dirty or corroded connection Check the connections at the wheel speed sensor connector the wheel speed sensor harness and the EHCU Electro Hydraulic Control Unit There may also be a problem in the wheel speed sensor or its associated tone toothed wheel Check for the proper air gap between the wheel speed sensor and tone wheel missing or broken teeth on the tone wheel a loose improperly mounted or mis adjusted wheel speed sensor 35 Left Rear Wheel Speed Sensor Circuit resistance is incorrect This code is indicative of high resistance in this particular wheel speed sensor circuit The resistance of the wheel speed sensor may be out of specification or there may be loose corroded or dirty connection
70. brake circuit an isolation valve and a dump valve Other types use a special two stage solenoid per brake circuit This two stage solenoid provides the same brake fluid control as the isolation and dump solenoids The isolation and dump solenoids have two positions coil off and coil fully energized The two stage solenoid has an additional position coil off coil partially energized and coil fully energized ABS computers controlling two stage type solenoids have special built in switching circuits to energize the solenoid properly Refer to How ABS Controls Brakes later in this section for a description of how the modulator is used Rotation Accumulator and Electric Pump These two components work together Depending upon system their use and construction will differ a great deal e Low Pressure type Accumulator and pump only used during ABS operation Accumulator acts as a reservoir It collects hydraulic fluid bled from brake circuit during ABS operation ABS relieves brake line pressure to avoid wheel lock up Four wheel ABS systems use two accumulators one for the rear wheel circuit and the other for the front wheel circuit The accumulator contains a moveable diaphragm which separates the inside into two chambers One chamber collects the hydraulic fluid The other side contains a spring pressing against the diaphragm Because
71. c System Operational This code is always sent 21 Right Front Wheel Speed Sensor circuit Checks for open shorted or intermittent condition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 22 Right Front Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 25 Left Front Wheel Speed Sensor circuit Checks for open shorted or intermittent condition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 26 Left Front Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 35 Rear Axle Speed Sensor circuit Checks for open shorted or intermittent condition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 36 Rear Axle Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 41 Right Front Solenoid Valve circuit This code will set if the physical position of the subject valve does not match the commanded position as given by the EBCM Electronic Brake Control Module 4
72. ceived Code 12 Computer found problems in vehicle along with other Follow steps in Section 4 Using Codes codes Code definitions are in Section 5 Code Meanings GM engine and transmission codes start on page 16 Saturn engine codes start on page 16 Saturn vehicles only Code 11 means transmission codes are flashed on Shift to D2 light Saturn transmission codes start on page 21 11 Using Codes Using Trouble Codes as Part of a Basic Troubleshooting Procedure A driveability problem can have many possible causes which are not related to the computer system Reading codes is one part of a good trouble shooting procedure consisting of 1 Visual Inspection 2 Basic Mechanical Checks 3 Reading Codes 4 Using the Vehicle Service Manual 5 Erasing Codes 1 Visual Inspection Doing a thorough visual and hands on underhood inspection before starting any diagnostic procedure is essential You can find the cause of many drivability problems by just looking thereby saving yourself a lot of time e Are routine maintenance items O K Clean air filter Correct fluid levels Recommended tire pressure Good ignition system components spark plugs wires and the like e Has the vehicle been serviced recently Sometimes things get recon nected in the wrong place or not at all e Dont take shortcuts Inspect hoses and wiring which may be di
73. connects end of coil to circuit ground Coil is ON because circuit is complete Coil connected to battery power and ground Transistor OFF Transistor disconnects end of coil from circuit ground Coil is OFF because circuit is open Coil not connected to circuit ground You can switch on most of the computer controlled relay and solenoid circuits except the fuel pump relay and fuel injectors This is helpful for checking relay operation or making wiring voltage checks Do the following 1 Safety First e Set the parking brake e Put shift lever in PARK automatic transmission or NEUTRAL manual transmission e Block the drive wheels e Make sure ignition key is in OFF position 2 Plug the Code Scanner into the Test Connector Put TEST switch on ENGINE A ee SOTA Transistor OFF 3 Turn Ignition Key to ON Position butDO NOT START THEENGINE Eld Service Test Fuel e WARNING Stay away from the Injected Engines Only radiator cooling fan It may turn On This is a quick check of the fuel control e Ignore the flashing Check Engine system to verify proper operation light especially after repair work Service manuals call this the Field Service Mode Do the following 4 Computer Controlled Relays and S Solenoids are Turned ON Exception Fuel pump and fuel 1 Safety First injectors are OFF Refer to vehicle e Set the parking brake service manua
74. ction 3 Reading Codes Check Engine Light Intermittent Problem Light ON and then goes OFF when the engine is RUNNING The computer saw a problem but the problem went away An intermittent failure Atrouble code is stored in computer memory An intermittent code The light went out because the problem went away but the code stays in memory Use the Code Scanner at the earliest convenient time to obtain codes Refer to Section 3 Reading Codes NOTE The computer will automati cally erase codes after several restarts typically 50 if the problem does not return A Poorly Running Engine No Check Engine light Most likely this condition is not due to computer system failures but reading codes can still be useful as part of a basic troubleshooting procedure Review Section 4 Using Codes before proceeding to Section 3 Reading Codes Reading Codes Using the Code Scanner to Read Codes 1 Safety First e Set the parking brake e Put shift lever in PARK automatic transmission or NEUTRAL manual transmission e Block the drive wheels e Make sure ignition key is in OFF position 2 Test the Check Engine Light Also called Service Engine Soon Service Engine Now or labeled with a small engine picture e Turn ignition key from OFF to ON position but do not start the engine e Verify that the light turns
75. cycle of 100 means the signal is always at a high value and not changing The engine control computer uses duty cycle type signals when it wants more than just on off control of an actuator This is how it works A 50 duty cycle signal going to a vacuum switching solenoid means the solenoid will be on passing full vacuum half the time and off passing no vacuum half the time The average amount of vacuum passing through the solenoid will be one half the full value because the solenoid is only on for one half the time The signal switches at a rapid rate such as ten times a second Thus the computer can get a vacuum controlled actuator to move half way between no vacuum position and full vacuum position Other positions can be achieved by changing the duty cycle of the control signal which in turn changes the average amount of control vacuum DVM Digital Volt Meter An instrument using a numeric readout to display measured voltage values as opposed to a moving needle on a gauge face Usually the instrument has other measuring capabilities such as resistance and current and may be called a DMM Digital Multi Meter Most DVM s have 10 Megohm input impedance This means the circuit under test will not be electronically disturbed when the DVM is connected for a measure ment ECM Electronic Control Module The brains of the engine control system lt is
76. depends upon vehicle Then ECM adjusts idle speed to prevent engine stalling when the A C system is engaged The ECM may also turn on the engine cooling fan A C Pressure sensor This sensor is connected to the A C refrigerant line It measures refrigerant pressure and sends a voltage signal to the ECM The ECM will turn off the A C system by de energizing the A C Clutch relay to prevent compressor damage if the pressure is too high or low A C Pressure switch This is a mechanical switch connected to the A C refrigerant line The switch is activated which sends a signal to the ECM when the A C refrigerant pressure becomes too low The ECM will turn off the A C system by de energizing the A C Clutch relay to prevent compressor damage Some vehicles have a second switch activated when the refrigerant pressure is too high Actuator Devices which are powered by the ECM to control things Actuator types include relays solenoids and motors Actuators allow the ECM to control engine operation A F Air fuel Air Injection Reaction AIR system This is an emission control system operated by the ECM During cold engine warm up an air pump injects outside air into the exhaust manifold to help burn hot exhaust gases This reduces pollution and speeds warm up of oxygen sensor and catalytic convertor After the engine is warm the air will either be dumped back to the atmosphere or into t
77. dule is the heart of the system It is sealed in a metal box and linked to the rest of the system by a wiring harness The computer module is located in the passenger compartment usually behind the dashboard or front kick panels This protects the electronics from moisture extreme temperatures and excess vibration which are common in the engine compartment The computer is permanently programmed by factory engineers The program is a complex list of instruc tions telling the computer how to control the engine under various driving conditions To do its job the computer needs to know what is happening and then it needs devices to control things Sensors give the computer information The computer can only work with electrical signals The job of the sensor is to take something the computer needs to know such as engine temperature and convert it to an electrical signal which the computer BRAINS OF THE COMPUTER can understand You can think of sensors as high tech senders the devices found in older vehicles for gauges and dashboard message lights oil pressure fuel level etc Signals running into the computer are referred to as inputs Sensors monitor such things as e Engine temperature e Intake manifold vacuum e Throttle position e RPM e Incoming air temperature amount e Exhaust gas oxygen content Most engine computer systems will use the sensor types listed above Additional senso
78. e Refer to the explanation under trouble code 41 81 Brake Stop Lamp switch circuit is shorted or open This code indicates a malfunction in the stop lamp switch circuit Note that this code can be set by a driver who rides the brake pedal 85 Anti lock indicator lamp circuit is open This code if present will be flashed by the brake warning lamp not the anti lock lamp and indicates an open circuit in the anti lock lamp circuit 86 Anti lock indicator lamp circuit is shorted This code if present will be flashed by the brake warning lamp not the anti lock lamp and indicates a short circuit in the anti lock lamp circuit Brake warning indicator lamp circuit is shorted This code indicates a short circuit in the brake warning indicator lamp circuit BUICK Century Electra Electra Wagon Estate Wagon Le Sabre Le Sabre Wagon Park Avenue Reatta Regal Regal Grand National Riviera Roadmaster Skyhawk Skylark Somerset CADILLAC Cimarron Roadmaster 5 7L CHEVROLET Beretta Camaro Caprice Cavalier Celebrity Chevette Citation Corsica Corvette El Camino Impala Lumina Monte Carlo Camaro 3 4L 5 7L Cavalier 3 1L Lumina 3 1L 1982 93 OLDSM OBILE Achieva Calais Custom Cruiser Cutlass Calais Cutlass Ciera Cutlass Cruiser Cutlass Cruiser Wagon Cutlass Supreme Cutlass Supreme Classic Delta 88 Eighty Eight Firenza Ninety Eight Omega Toronado Touring S
79. e Control Module There is a motor monitoring circuit in the EBCM which will detect a defective relay or a failure in the associated circuitry 71 EBCM Electronic Brake Control Module failure This code will set if there is an internal failure of the Electronic Brake Control Module SYSTEM 4 Bosch 2U Version C 1993 Eldorado Seville 1994 DeVille Eldorado Seville Pre Diagnostic Visual Inspection Complete all steps before reading trouble codes 1 Check that all ABS system grounds are clean and tight Check the ground that is located on the bottom left side of the engine block near the transaxle Check the ground that is located on the left rear seat brace 2 Check power sources which supply various parts of ABS system Check fuse A1 10 amp in the trunk compartment fuse block This fuse provides switched power to the EBCM Check fuse B3 20 amp in the engine compartment fuse block This fuse provides continuous power to the brake light switch Check fuse A3 10 amp in the engine compartment fuse block This fuse provides switched power to the amber anti lock indicator lamp Check fuse 5 50 amp in the right MAXI fuse block This fuse provides continuous power to the relays in the brake pressure modulator valve assembly Check the fusible links on the junction block 70 3 Check that all ABS TCS connec tors and EBTCM Electronic Brake and Traction C
80. e Meanings Bosch 2U Version C IMPORTANT Always follow vehicle service manual procedures for any ABS repairs 12 Diagnostic System Operational This code is always sent 21 Right Front Wheel Speed Sensor circuit Checks for open shorted or intermittent condition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 22 Right Front Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 23 Right Front Wheel Speed Sensor Continuity fault Checks for open or shorted condition in subject circuit The ignition must be on and the vehicle not moving for this code to set 25 Left Front Wheel Speed Sensor circuit Checks for open shorted or intermittent condition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 26 Left Front Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 27 Left Front Wheel Speed Sensor Continuity fault Checks for open or shorted condition in subject circuit The ignition must be on and the vehicle not moving for this code to set 31 Right Rear Wheel Speed Sensor circuit Checks for open shorted or intermittent cond
81. eanings Bosch 2U Version B IMPORTANT Always follow vehicle service manual procedures for any ABS repairs 12 Diagnostic System Operational This code is always sent 21 Right Front Wheel Speed Sensor circuit Checks for open shorted or intermittent condition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 22 Right Front Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 25 Left Front Wheel Speed Sensor circuit Checks for open shorted or intermittent condition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 26 Left Front Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 31 Right Rear Wheel Speed Sensor circuit Checks for open shorted or intermittent condition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 32 Right Rear Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 35 Left Rear Wheel Speed Sensor circuit Checks for open shorted o
82. ection e Refer to the vehicle service manual diagnostic code section You can not use the code chart procedures because they are for hard problems those which are present now However the charts have suggestions for dealing with intermittents and can tell you where bad connections etc might exist You can also refer to the Diagnosis by Symptom charts e Be sure to erase the trouble codes from computer memory after completing repair work See Step 5 Erasing Codes from Computer Memory e Drive vehicle for at least 10 minutes at normal temperature cruise speed and load Read codes again to verify trouble code is gone problem fixed Other codes may have been repaired at the same time Dealing with No Trouble Codes Have a driveability problem but only get code 12 Make sure you do Step 1 Visual Inspection and Step 2 Basic Mechanical Checks If you did not find the problem then refer to Diagnosis by Symptom charts in vehicle service manual 5 Erasing Codes from Computer Memory Erase codes from memory whenever you complete a repair or to see if a problem will occur again Note The computer will automatically erase codes after several restarts typically 50 if the problem does not return Proceed as follows e Observe all safety precautions See page 4 e Turn ignition key ON e Insert Code Scanner Make sure TEST switch is in ENGINE position
83. ectric circuit to another causing a change in the normal current flow path Solenoid A device to convert an electrical signal to mechanical motion It consists of a coil of wire with a movable metal rod in the center When power is applied to the coil the resulting electromagnetism moves the rod and performs some mechanical action The ECM often uses solenoids to switch vacuum lines on and off This allows the ECM to control vacuum operated devices such as an EGR valve Fuel injectors are another type of solenoid Stepper Motor A special type of electric motor with a shaft that rotates in small steps instead of a continuous motion A certain sequence of frequency type signals is required to step the motor shaft A different signal sequence will step the shaft in the opposite direction No signals keeps the shaft still in position A constant signal drive will continuously rotate the shaft The shaft is usually connected to a threaded assembly which moves back and forth to control things such as idle speed bypass air flow see IAC The engine computer sends the correct signals to the motor for control TBI Throttle Body Injection A fuel injection system having one or two injectors mounted in a centrally located throttle body as opposed to positioning the injectors close to an intake valve port TCC solenoid Torque Convertor Clutch solenoid The ECM uses this solenoid to control the lock up c
84. ectronic Brake Control Module Note This code may also be sent along with Code 51 which has the same meaning 72 Right Front Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 52 which has the same meaning 80 73 Right Rear Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 53 which has the same meaning 74 Left Rear Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 54 which has the same meaning 75 Left Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 76 Right Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 77 Right Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 78 Left Rear Wheel Speed Sensor circuit Checks for an open short or intermitte
85. ed Sensor circuit Checks for open shorted or intermittent condition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 26 Left Front Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 31 Right Rear Wheel Speed Sensor circuit Checks for open shorted or intermittent condition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 32 Right Rear Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 35 Left Rear Wheel Speed Sensor circuit Checks for open shorted or intermittent condition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 36 Left Rear Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 41 Right Front Solenoid Valve circuit This code will set if the physical position of the subject valve does not match the commanded position as given by the EBCM Electronic Brake Control Module 45 Left Front Solenoid Valve circuit This code will set if the physical
86. ed these tests for years Now you can do the same thing by using the Code Scanner tool Engine computers perform special tests The engine computer runs the special tests The type of testing varies with manufacturer engine model year etc There is no universal test that is the same for all vehicles The tests examine INPUTS electrical signals going IN to the computer and OUTPUTS electrical signals coming OUT of the computer Input signals which have wrong values or output circuits which don t behave correctly are noted by the test program and the results are stored in the computer s memory These tests are important The computer can not control the engine properly if it has bad inputs or outputs Code numbers give test results The test results are stored by using code numbers usually called trouble codes or diagnostic codes For example a code 22 might mean throttle position sensor signal voltage is too low Code meanings are listed in Section 4 Specific code definitions vary with manufacturer engine and model year so you may want to refer to a vehicle service manual for additional information These manuals are available from the manufacturer other publishers or your local public library Read Codes with the Code Scanner You obtain trouble codes from the engine computer memory by using the Code Scanner tool Refer to section 2 for details After you get the trouble codes yo
87. edan Trofeo 1994 PONTIAC 6000 6000 STE Bonneville Fiero Firebird Grand Am Grand Prix J2000 LeMans Parisienne Phoenix Safari Safari Wagon Sunbird T1000 SATURN All models Firebird 3 4L 5 7L All models Sunbird 2 0L 3 1L TRUCKS amp VANS All gasoline burning vehicles 1 ton capacity or less All gasoline burning vehicles 1 ton capacity or less 1995 Code Scanner is only applicable if vehicle DOES NOT HAVE a climate control computer SUOHLII ddy 12UULDS Bpod IND GM ABS Applications Chevrolet Oldsmobile YEAR 1989 90 1989 90 1989 91 1989 93 1991 1990 92 1989 90 1989 93 1989 90 1989 93 1991 1990 91 1989 90 1991 1989 90 1989 92 1990 92 1989 90 MODEL Electra Park Avenue Reatta Riviera Roadmaster Brougham DeVille Eldorado Fleetwood Seville Caprice Corvette 98 Regency Custom Cruiser Delta 88 Toronado Trofeo Bonneville MAKE Chevrolet GM Van MAKE Chevrolet YEAR 1990 93 MODEL 1989 93 Astro G Series TRUCKS YEAR 1988 93 1990 93 1988 94 1988 94 1990 91 1989 94 1990 94 1990 91 1989 93 1989 93 1988 93 1991 93 1991 93 1992 93 1992 93 MODEL Blazer Suburban C Series K Series R Series S Series T Series V Series Jimmy Safari Sierra Sonoma Syclone Typhoon Yukon Oldsmobile 1991 93 Bravada Vehicles not listed may be tested for engine transmission trouble codes only 1989
88. embly or a failure in the front axle transfer case switch or its associated wiring and or connectors 6 Erratic Vehicle Speed Sensor signal This code indicates either a defective or erratic vehicle speed sensor check for engine diagnostic trouble code 24 defective DRAC Digital Ratio Adapter Controller or its circuitry or any associated wiring An open battery feed fuse to the ABS electronic control module could also cause this code to set 7 Shorted Isolation valve or defective ECM Electronic Control Module This code indicates a shorted circuit in the isolation valve or associated wiring The anti lock brake system control module may also have failed Shorted Dump valve or defective ECM Electronic Control Module This code indicates a shorted circuit in the dump valve or associated wiring The anti lock brake system control module may also have failed 9 Open circuit to the Vehicle Speed Sensor signal This code indicates a defective vehicle speed sensor check for engine diagnostic trouble code 24 defective DRAC Digital Ratio Adapter Controller or its circuitry or any of its associated wiring An open battery feed fuse to the ABS electronic control module could also cause this code to set 89 10 Stop Brake Light circuit This code indicates a missing stop light signal from the stop light switch The stop light switch may be mis adjusted or defective or there may be a pr
89. ervice manual 76 If the anti lock lamp is ON and the brake warning lamp is ON refer to the proper diagnostic chart in the vehicle service manual If the anti lock lamp is OFF and the brake warning lamp is OFF then this indicates normal system operation or an intermittent problem Intermittent trouble codes may or may not be stored Reading ABS Codes Teves Mark Il Version A IMPORTANT Perform all steps in PRE DIAGNOSTIC VISUAL INSPEC TION and FUNCTIONAL CHECK before reading ABS codes 1 Safety First e Set the parking brake e Put shift lever in PARK automatic transmission or NEUTRAL manual transmission e Block the drive wheels e Make sure ignition key is in OFF position 2 Verify Codes are Stored e Turn the ignition key to the ON position but do not start the engine e Wait 30 seconds e Observe anti lock light Light ON Codes are stored Proceed with testing Light OFF No codes are stored Stop testing e Turn ignition key OFF 3 Have a Pencil and Paper Ready This is for writing down all the codes 4 Find the Computer Test Connector e Service manuals call this connector the Assembly Line Diagnostic Link ALDL connector It may also be called the Assembly Line Commu nication Link ALCL or simply test onnector e The connector is located under the dashboard on the driver s side e The connector may be in full view or it may be recessed behind a p
90. es in the cylinders and this reduces poisonous NOx emissions The computer controls the flow of gases through the EGR valve The EGR system is only used during warm engine cruise conditions A partially open EGR valve at other times can cause Stalling Various types of EGR systems are used on different vehicles The EGR valve may be operated by engine vacuum or with a computer controlled electrical or vacuum signal See EGR in Glossary Section 8 for more details e Air Injection System This system reduces harmful carbon monoxide CO and hydrocarbon HC emissions The computer takes outside air from an air pump and directs it to the exhaust manifold during engine warm up The extra air helps partially burned exhaust gases to completely burn and reduce pollution After warm up depending upon vehicle the air pump may send air down to the catalytic convertor or dump it back to the atmosphere Various types of Air Injection systems are used on different vehicles Refer to Air Injection System in Glossary Section 8 for more explanation e Fuel Evaporation Recovery System A special canister collects vapors evaporating from the fuel tank preventing them from escaping into the atmosphere and causing pollution During warm engine cruise conditions the computer opens a connection between the cannister and the engine by energizing the Purge solenoid Then engine vacuum draws the trapped fuel vapors into
91. essure reduction command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 52 which has the same meaning 73 Right Rear Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 53 which has the same meaning 74 Left Rear Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 54 which has the same meaning SYSTEM 7 Kelsey Hayes RWAL Rear Wheel Anti Lock 1988 Blazer C 4 K Series Pickup Truck Sierra 1989 Astro Blazer C amp K Series Pickup Truck Jimmy S Series 2 WD Pickup Truck Safari Sierra 1990 Astro Blazer C amp K Series Pickup Truck G Series RWD Van Jimmy R 8 V Series Truck S 8 T Series Pickup Truck Safari Sierra Suburban 1991 Astro Blazer C amp K Series Pickup Truck G Series RWD Van Jimmy R 8 V Series Truck S 8 T Series Pickup Truck Safari Sierra Suburban 1992 Astro Blazer C 4 K Series Pickup Truck G Series RWD Van Jimmy S 8 T Series Pickup Truck Safari Sierra 1993 Blazer C amp K Series Pickup Truck Jimmy S 8 T Series Pickup Truck Sier
92. feres with the wheel sensor can create intermittent problems or set trouble codes Note the following Do not mix tire sizes Rolling diameter must be the same for all four tires Differently sized tires or using a compact spare can cause inaccurate wheel speed sensor operation Do not tap the speed sensor or toothed sensor ring Tapping these parts can disturb their magnetic properties and upset wheel speed sensor operation Press do not hammer toothed sensor ring onto hub if service is required Do not overtighten wheel lug nuts Specifications are in vehicle service manual Brake drum or rotor may bend causing inaccurate wheel speed sensor operation Do not coat wheel speed sensor parts with grease Refer to vehicle service manual for recommended material Check spacing between wheel speed sensor and toothed ring especially after servicing Incorrect spacing can cause faulty sensor operation Specifications are in vehicle service manual Check for cracked or missing teeth on the wheel speed sensor ring Spinning tires or axle on a stationary vehicle during a service procedure may set ABS trouble codes IMPORTANT Always follow vehicle service manual procedures for any ABS repairs e Radio transmitters can interfere with operation of ABS computer Keep antenna wiring from a CB radio or portable telephone away from ABS wiring e Check ABS power circuits Make sure vehicle a
93. fficult to see because of location beneath air cleaner housings alternators and similar components e Inspect all vacuum hoses for Correct routing Hoses may be missing or misconnected Refer to vehicle service manual or Vehicle Emission Control Information VECI decal located in the engine compart ment Pinches and kinks Splits cuts or breaks e Inspect wiring for Contact with sharp edges This happens often Contact with hot surfaces such as exhaust manifolds Pinched burned or chafed insulation Proper routing and connections e Check electrical connectors for Corrosion on pins Bent or damaged pins Contacts not properly seated in housing Bad wire crimps to terminals Problems with connectors are common in the engine control system Inspect carefully Note that some connectors use a special grease on the contacts to prevent corrosion Do not wipe off Obtain extra grease if needed from your vehicle dealer It is a special type for this purpose 2 Basic Mechanical Checks Don t overlook the basic checks listed on the next page Mechanical problems by themselves can always create engine troubles Even worse these problems can make a good sensor send an incorrect signal to the computer Then the computer runs the engine improp erly or sets a trouble code e Cylinder compression Check for proper compression in each
94. g fan It may turn FLASH pause FLASH FLASH on even longer pause then start over again 8 Get Codes from gain the Flashing Anti Lock Light e Count flashes to get trouble codes Flashes begin after a few seconds 60 Example of code series 12 and 24 9 Turn Ignition Key OFF JC PAUSE XEXE FLASH pause FLASH FLASH longer pause al gt se PAUSE ATA FLASH pause FLASH FLASH 10 Remove Code Scanner and Re longer pause install Connector Cover if supplied AN PAUSE ASAE The computer system is now back to FLASH pause FLASH FLASH BESSER even longer pause then go to next 11 Refer to ABS Code Meanings on code page 63 Bosch 2U Version A This completes the code reading NUNN INT e EE procedure FLASH FLASH pause At this point you can either FLASH FLASH FLASH FLASH e Have your vehicle professionally serviced Trouble codes indicate longer pause problems found by the computer NUNN ENT G PAUSE 78 gt 8S TOS TN or FLASH FLASH pause e Repair the vehicle yourself using FLASH FLASH FLASH FLASH trouble codes to help pinpoint the problem longer pause IMPORTANT Always follow vehicle ale MS ur SNA a PAUSE FON IN TN service manual procedures for any ASE pause ARS Neen FLASH FLASH FLASH FLASH even longer pause then start all over from the very beginning e Acode 12 is always sent even when the computer sees no problem This tells you the computer d
95. gency Park Avenue Pre Diagnostic Visual Functional Check Inspection 1 Turn the ignition key to the ON Complete all steps before reading position but do not start the engine trouble codes 2 The anti lock lamp should illuminate 1 Check brake fluid level for at least 3 seconds If it does not refer to the proper diagnostic chart in the vehicle service manual 2 Release the parking brake if it is set 3 Observe the anti lock and brake lamps while starting the engine ignition key is in the cranking position Both the anti lock and brake lamps should be 4 Check system ON during electrical connections cranking H they Wheel speed sensor connectors are dia Se SE i proper diagnostic chart in the vehicle EBCM Electronic Brake Control senice manual Module connectors System relay connectors 3 Check all ABS system fuses Syst d 4 When the engine starts allow it to SSI nee run for 30 seconds and then turn it OFF for 10 seconds This completes the visual inspection Perform FUNCTIONAL CHECK before 5 Return the ignition key to the ON reading codes position do not start the engine and wait 10 seconds Observe the condition of the anti lock and brake warning lamps If the anti lock lamp is ON and the brake warning lamp is OFF proceed to READING ABS CODES page 77 If the anti lock lamp is OFF and the brake warning lamp is ON refer to the proper diagnostic chart in the vehicle s
96. gines 65 Large EGR failure OR Fuel injector current low OR Right oxygen O sensor rich condition indicated dual sensor engines OR Cruise control position sensor problem 66 Air Conditioner A C pressure sensor circuit problems or low A C charge OR Electronic Control Module ECM computer circuit problem internal reset occurred OR Transmission 3 2 shift control solenoid circuit problems 67 Cruise control switch circuit problems OR Air Conditioner A C pressure sensor circuit problems OR Torque Converter Clutch TCC solenoid circuit problems OR Cruise control switches circuit problems 68 Cruise control system circuit problems OR Air Conditioner A C clutch relay short circuit OR Transmission Overdrive ratio error engine RPM greater than input speed 69 Air Conditioner A C system pressure switch or A C clutch relay circuit problems OR Torque converter clutch stuck on 70 Air Conditioner A C pressure sensor signal voltage too high 71 Air Conditioner A C evaporator temperature sensor signal voltage too low 72 Gear Select switch circuit problems OR 19 Vehicle Speed Sensor VSS loss of signal 73 Air Conditioner A C evaporator temperature sensor signal voltage too high OR Transmission Pressure control solenoid circuit problems 74 Traction control circuit
97. h case your defective unit has value core credit towards the purchase of the replacement Securely attach a tag to your defective unit clearly indicating the trouble code s reported by the defective EHCU 43 44 47 48 53 54 amp 68 all at the same time If all of these codes appear simultaneously carefully check all power and ground connections at the EHCU Electro Hydraulic Control Unit 44 Right Front Pulse Width Modulation Valve Solenoid short circuit Refer to the explanation under trouble code 43 45 Left Front Isolation Valve Solenoid open circuit Refer to the explanation under trouble code 41 46 Left Front Pulse Width Modulation Valve Solenoid open circuit Refer to the explanation under trouble code 41 47 Left Front Isolation Valve Solenoid short circuit Refer to the explanation under trouble code 43 48 Left Front Pulse Width Modulation Valve Solenoid short circuit Refer to the explanation under trouble code 43 51 Rear Isolation Valve Solenoid open circuit Refer to the explanation under trouble code 41 52 Rear Pulse Width Modulation Valve Solenoid open circuit Refer to the explanation under trouble code 41 53 Rear Isolation Valve Solenoid short circuit Refer to the explanation under trouble code 43 54 Rear Pulse Width Modulation Valve Solenoid short circuit Refer to the explanation under trouble code 43 61 Right Front Reset Sw
98. haft sensor circuit problems OR Electronic Control Module ECM computer circuit problem Pull up resistor Saturn 18 Camshaft or Crankshaft sensor circuit problems OR Fuel Injector circuit is not working properly possible blown fuel injector fuse 19 Ignition system fault Intermittent 7X signal or loss of 58X signal or 6X signal Saturn 21 Throttle position sensor TPS signal voltage is high during engine idle or deceleration 22 Throttle position sensor TPS signal voltage is low during engine idle OR Fuel cutoff relay circuit open or shorted to ground 23 Manifold air temperature MAT sensor signal voltage is low or high OR Throttle position sensor TPS error OR Mixture Control M C solenoid open or short circuit problems 24 Vehicle speed sensor VSS open or short circuit problems 25 Manifold air temperature MAT sensor signal voltage is low OR Vacuum switching valve circuit open or shorted to ground OR ATS sensor signal voltage is high 26 Quad Driver module or Quad driver No 1 error 27 2nd gear switch OR Quad Driver module or Quad driver No 2 error 28 3rd gear switch OR Quad Driver module or Quad driver No 3 error Corvette OR Transmission Fluid pressure switch assembly open or short circuit problems 29 4th gear switch OR Quad Driver module or Quad driver No 3 err
99. he air cleaner or sent into the catalytic convertor There are various versions of the AIR system depends upon vehicle The air pump is usually belt driven by the vehicle engine The ECM controls air flow from the pump by operating two electrically powered solenoid valves An Electric Air Divert Valve either dumps the air to atmosphere valve unpowered or sends the air further into the system valve energized A second control valve the Air Switching Valve routs the air to the catalytic convertor valve unpowered or to the exhaust manifold valve energized These two valves may be individual components or combined into one assembly The ECM normally sends air to the catalytic convertor during warm engine operation The ECM will divert air away from the convertor to prevent overheating damage under certain operating conditions such as decel high RPM or rich air fuel conditions 33 Some vehicles have an electrically powered air pump controlled by the ECM This system injects air into the exhaust manifold only when the pump is energized and running No air is injected when the pump is off The air pump does not send air to the catalytic convertor in this version ALDL Assembly Line Diagnostic Link This is the connector that the Code Scanner plugs into for testing purposes The connector is wired to the ECM and is usually located under the dashboard on the driver s side BARO
100. hen to Read Codes 7 3 Reading Codes cccccceeeeeees 8 4 Using Codes in a Basic Troubleshooting Procedure 12 5 Code Meanmgs 16 6 Additional Code Scanner Diagnostic Features 24 7 Computer Basics o 27 8 Glossary cscerincmcaserson remontamos 33 Anti Lock Brake ABS Section 9 ABS Basics mesonenicua tii 40 10 ABS Safety occcccccccccncccccncccccnnonnss 46 11 ABS TIOS E 47 12 Reading ABS Codes 0000nnnnn 49 System 1 Bosch 29 socorro 53 System 2 Bosch 2U Version A 58 System 3 Bosch 2U Version B 64 System 4 Bosch 2U Version C 70 System 5 Teves Mark II Version A 76 System 6 Teves Mark II Version B 81 System 7 Kelsey Hayes RWAL 86 System 8 Kelsey Hayes 4WAL 90 Applications ooccccocccccccconccaanonnnnas 96 Instrucci nes en espa ol 99 General Safety Guidelines to follow when working on vehicles e Always wear approved eye protection e Always operate the vehicle in a well ventilated area Do not inhale exhaust gases they are very poisonous Always keep yourself tools and test equipment away from all moving or hot engine parts e Always make sure the vehicle is in park Automatic transmis sion or neutral manual transmission and that the parking brake is firmly set Block the drive wheels e Never leave vehicle unattended while running tests e Never lay tools on veh
101. here you will find e preliminary checks you need to make before reading codes e the code reading procedure e the procedure for erasing codes from ABS computer memory e alist of code definitions Model System Model System Blazer ES 86 98 Regency 5 76 C Series Astro 7 86 Pickup Truck 7 86 Blazer gt 86 lo ele 7 86 Bonneville 5 76 Siena 7 86 Bonneville SSE 5 76 C Series Pickup Truck 7 86 Delta 88 5 76 DeVille 5 76 Eldorado 6 81 Electra 5 76 Fleetwood 5 76 Jimmy E 86 K Series Pickup Truck T 86 Park Avenue 5 76 Reatta 6 81 Riviera 6 81 S Series 2WD Pickup Truck 7 86 Safari 7 86 Seville 6 81 Sierra 7 86 Toronado 6 81 49 Model System 98 Regency 5 76 Astro 7or8 See note p 52 Blazer 7 86 Bonneville 5 76 Bonneville SSE 5 76 Brougham 2 58 C Series Pickup Truck 7 86 Corvette 1 53 Delta 88 5 76 DeVille 5 76 Eldorado 6 81 Electra 5 76 Fleetwood 5 76 G Series RWD Van 86 Jimmy 7 86 K Series Pickup Truck 7 86 Park Avenue 5 76 R Series Truck 7 86 Reatta 6 81 Riviera 6 81 S Series Pickup Truck 7 86 Safari 7or8 See note p 52 Seville 81 Sierra 86 Suburban 86 T Series Pickup Truck 7 86 Toronado 6 81 Trofeo 6 81 V Series Truck 7 86 50 Model Astro Blazer Bravada Brougham C Series Pickup Truck Caprice Corvette Custom Cruiser Eldorado G Series RWD Van Jimmy K Series Pickup Truck R Series Truck Reatta Riviera Roadmaster S Series Pickup Truck Safari Seville
102. iagnostic checks are working properly e All codes are two 2 digits long 61 Erasing ABS Codes from Computer Memory Bosch 2U Version A Erase codes from memory whenever you complete a repair or to see if a problem will occur again Note The computer will automatically erase codes after several restarts typically 100 if the problem does not return Proceed as follows 1 Turn the ignition switch to the ON position b The anti lock ur lamp should GE y turn OFF after 3 to 4 seconds If it does not a failure still currently exists which must be corrected before its corresponding trouble code will clear 2 Plug the Code Scanner make sure the TEST switch is in the ABS position into the test connector Sa CES Wi UR 3 Remove the Code Scanner for about 1 second then reinstall Code Scanner into the connector Repeat this procedure 4 times within 10 seconds Leave the Code Scanner inserted in the connector after the 4th time Observe the anti lock indicator lamp 4 Code 12 the diagnostic system operational code should flash indicating that all trouble codes have been erased from memory Wait at least 15 seconds before turning the ignition switch OFF Remove the Code Scanner and reinstall the test connector cover if used on vehicle ABS Code Meanings Bosch 2U Version A IMPORTANT Always follow vehicle service manual procedures for any ABS repairs 12 Diagnosti
103. icle battery You may short the terminals together causing harm to yourself the tools or the battery e Never smoke or have open flames near vehicle Vapors from gasoline and charging battery are highly flam mable and explosive Always keep a fire extinguisher suitable for gasoline electrical chemical fires handy e Always turn ignition key OFF when connecting or disconnect ing electrical components unless otherwise instructed Always follow vehicle manufacturer s warnings cautions and service procedures CAUTION Some vehicles are equipped with safety air bags You must follow vehicle service manual cautions when working around the air bag components or wiring If the cautions are not followed the air bag may open up unexpectedly resulting in personal injury Note that the air bag can still open up several minutes after the ignition key is off or even if the vehicle battery is disconnected because of a special energy reserve module About Codes Where do they come from and what are they for Engine computers can find problems The computer system in today s vehicles does more than control engine operation it can help you find problems too Special testing abilities are permanently programmed into the computer by factory engineers These tests check the components connected to the computer which are used for typically fuel delivery idle speed control spark timing and emission systems Mechanics have us
104. ied by an electronic signal from the ECM The signal controls a mixture control solenoid MCS attached to the carburetor body Frequency The frequency of an electronic signal is a measure of how often the signal repeats a voltage pattern in a one second time span For example suppose a signal starts at zero volts goes to five volts then returns to zero again If this pattern repeats itself 100 times in one second then the signal frequency is 100 cycles per second or 100 Hertz Fuel Injector An electronically controlled flow valve Fuel injectors are connected to a pressurized fuel supply The pressure is created by a fuel pump No flow occurs when the injector is off not energized When the injector is powered it opens fully allowing the fuel to flow The ECM controls fuel delivery by varying the amount of time the injectors are turned on Fuel Pump Relay The ECM energizes this relay to apply power to the vehicle fuel pump For safety reasons the ECM removes power from the fuel pump when ignition signals are not present Fuel Pump Signal This is a wire between the ECM and the fuel pump motor power terminal The ECM uses this signal to verify when voltage is at the fuel pump for diagnosing fuel pump problems Gear switches These are switches usually two located inside certain automatic transmissions The ECM monitors the switches to determine what transmission gear is engaged
105. in full view or it may be recessed behind a panel opening e The connector may have a slip on cover labeled Diagnostic Connector Remove cover for testing Replace cover after testing Some vehicles require this cover in place for proper operation Oy 4 Verify Ignition Key is OFF JN 71 5 Put the TEST switch on ABS 6 Plug the Code Scanner into the test connector e The Code Scanner only fits ONE WAY into the test connector e The Code Scanner will not harm the vehicle computer Note The Code Scanner does not use all of the test connector contacts This is normal 7 Turn Ignition Key to ON Position but DO NOT START de THE ENGINE WARNING Stay away from the radiator cooling fan It may turn on 8 Get Codes from the Flashing Anti Lock Light e Count flashes to get trouble codes Flashes begin after a few seconds Code 12 looks like ale lp xl SAS SS FLASH pause FLASH FLASH FLASH 1 FLASH FLASH 2 Put 1 and 2 together code 12 Code 23 looks like st 2 als alt sv pais POS PAUSE SiS OS Ons FLASH FLASH pause FLASH FLASH FLASH e Each code is flashed three 3 times before the next trouble code is sent e After all codes are sent the whole sequence is repeated This continues until the ignition key is turned OFF so you can double check your code list Example of code 12 only y Se S PAUSE 79787 FLASH pause FLASH FLASH
106. itch open circuit Refer to the explanation under trouble code 41 62 Left Front Reset Switch open circuit Refer to the explanation under trouble code 41 63 Rear Reset Switch open circuit Refer to the explanation under trouble code 41 65 Pump Motor Relay open circuit Refer to the explanation under trouble code 41 IMPORTANT This code may be FALSELY set by an improperly performed trouble code clearing procedure 66 Pump Motor Relay short circuit Refer to the explanation under trouble code 41 67 Pump Motor Circuit open circuit This code indicates an open circuit in the connection between the pump motor and the EHCU Electro Hydraulic Control Unit 68 Pump Motor Circuit shorted circuit This code indicates a shorted circuit in the connection between the pump motor and the EHCU Electro Hydraulic Control 95 Unit Carefully check all power and ground connections at the EHCU 71 EHCU Electro Hydraulic Control Unit has a RAM Random Access Memory error Refer to the explanation under trouble code 41 72 EHCU Electro Hydraulic Control Unit has a ROM Read Only Memory error Refer to the explanation under trouble code 41 73 EHCU Electro Hydraulic Control Unit has an internal circuit error Refer to the explanation under trouble code 41 74 EHCU Electro Hydraulic Control Unit has an internal circuit error which is causing excessive isolation tim
107. ition as given by the EBTCM Electronic Brake and Traction Control Module 45 Left Front Solenoid Valve circuit This code will set if the physical position of the subject valve does not match the commanded position as given by the EBCM Electronic Brake Control Module 48 Left Front Traction Control System Pilot Valve fault This code will set if the physical position of the subject valve does not match the commanded position as given by the EBTCM Electronic Brake and Traction Control Module 51 Right Rear Solenoid Valve circuit This code will set if the physical position of the subject valve does not match the commanded position as given by the EBCM Electronic Brake Control Module 55 Vehicles with Traction Control Left Rear Solenoid Valve circuit This code will set if the physical position of the subject valve does not match the commanded position as given by the EBTCM Electronic Brake and Traction Control Module 55 Vehicles without Traction Control Rear ABS Solenoid Valve circuit This code will set if the physical position of the subject valve does not match the commanded position as given by the EBCM Electronic Brake Control Module 61 Pump Motor or Motor Relay circuit This code will set if the position of the motor relay contacts do not match the commanded position of those contacts as given by the EBCM Electronic Brake Control Module There is a motor mon
108. ition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 32 Right Rear Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 33 Right Rear Wheel Speed Sensor Continuity fault Checks for open or shorted condition in subject circuit The ignition must be on and the vehicle not moving for this code to set 35 Left Rear Wheel Speed Sensor circuit Checks for open shorted or intermittent condition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 36 Left Rear Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 74 37 Left Rear Wheel Speed Sensor Continuity fault Checks for open or shorted condition in subject circuit The ignition must be on and the vehicle not moving for this code to set 41 Right Front Solenoid Valve circuit This code will set if the physical position of the subject valve does not match the commanded position as given by the EBCM Electronic Brake Control Module 44 Right Front Traction Control System Pilot Valve fault This code will set if the physical position of the subject valve does not match the commanded pos
109. itoring circuit in the EBCM which will detect a defective relay or pump motor 63 Solenoid Valve Relay circuit This code will set if the position of the valve relay contacts do not match the commanded position of those contacts as given by the EBCM Electronic Brake Control Module There is a motor monitoring circuit in the EBCM which will detect a defective relay or a failure in the associated circuitry 67 Brakelight Switch circuit Vehicles with Traction Control This code will set if the brakelight switch signal is not received 75 71 EBCM or EBTCM Electronic Brake Control or Traction Control Module failure This code will set if there is an internal failure of the Electronic Brake Control Module 73 EBTCM Electronic Brake and Traction Control Module PWM Pulse Width Modulated Signal failure 4 6 Liter engine only This code will set if there is a desired torque level signal communication failure between the EBTCM Electronic Brake and Traction Control Module and the PCM Powertrain Control Module 83 Low Brake Fluid Level Vehicles with Traction Control This code will set if the brake fluid level is low or there is a problem with the brake fluid level sensing system SYSTEM 5 Teves Mark II Version A 1989 Bonneville Bonneville SSE Delta 88 DeVille Electra Fleetwood 98 Regency Park Avenue 1990 Bonneville Bonneville SSE Delta 88 DeVille Electra Fleetwood 98 Re
110. k ALCL or simply test connector e The connector is located under the dashboard on the driver s side e The connector may be in full view or it may be recessed behind a panel opening e The connector may have a slip on cover labeled Diagnostic Connector Remove cover for testing Replace cover after testing Some vehicles require this cover in place for proper operation 4 Verify Ignition Key is OFF Code 12 looks like ale ale ale Av PAUSE WOW FLASH pause FLASH FLASH FLASH 1 FLASH FLASH 2 Put 1 and 2 together code 12 5 Put the TEST switch on ABS Code 23 looks like 6 Plug the Code See See PAUSE Se Seek rta me FLASH FLASH pause conrector FLASH FLASH FLASH i e Each code is flashed three 3 Deeg N times before the next trouble code only fits is sent ONE WAY e After all codes are sent the whole into the test sequence is repeated This connector continues until the ignition key is turned OFF so you can double e The Code Scanner will not harm i check your code list the vehicle computer Note The Code Scanner does not Example of code 12 only use all of the test connector contacts This is normal AE al gt Av PAUSE IAS FLASH pause FLASH FLASH 7 Turn longer pause Ignition Key to ON Set PAUSE 392 S06 cio ON FLASH pause FLASH FLASH START THE wp longer pause ENGINE on Te Dean WARNING Stay away from the AN py py radiator coolin
111. l for any other e Put shift lever in PARK automatic exceptions transmission or NEUTRAL e Make any relay or manual transmission solenoid circuit checks at this time Note the e Block the drive wheels e Make sure ignition key is in OFF following special position circuit actions Fuel Injected 2 Test the Check Engine Light Engines Only Also called The Idle Air Service Engine Soon Service Engine Now or labeled with a small engine picture e Turn ignition key from OFF to ON position but do not start the engine Control IAC motor fully extends most vehicles or moves back and forth Carbureted Engines Only The Idle Speed Control ISC motor if used on vehicle moves back and forth Also the Exhaust Gas Recirculation EGR solenoid is energized for 25 seconds e If the light does not turn on you have a problem with this circuit A which must be repaired before 5 Turn Ignition Key OFF proceeding Refer to the Diagnos e Remove Code Scanner and re tic Circuit Check procedure in your install connector cover if supplied vehicle service manual e Verify that the light turns on e The computer system is now back to normal e This completes the Relay and Solenoid Circuit Test 3 Start the Engine WARNING Always operate vehicle in well ventilated area Exhaust gases are very poisonous 4 Plug the Code Scanner into the Test Connector Put
112. led Electronic Brake Control Module EBCM or similar The computer monitors wheel speed acceleration and deceleration using signals sent by the wheel speed sensors If the computer determines wheel lock up is likely during braking it will control brake pressure using the Hydraulic Control Modulator ABS components and braking operation will be detailed later in this section As a safety feature the system reverts to normal hydraulic braking operation if the ABS computer cannot operate Rear Wheel Speed Sensors e Go E Hydraulic Control MS Modulator SN V ch De G Electronic Brake S Eet Control Unit ABS computer Courtesy of General Motors Corp Typical 4 Wheel Anti Lock Brake System 40 ABS Types There are three basic types e RWAL Rear Wheel Anti Lock This is the simplest ABS system mostly used on small rear wheel drive trucks Only the rear wheels are ABS controlled not the front This version stops the vehicle in a straight line but does not allow the driver to maneuver because the front wheels may lock A single speed sensor usually mounted in the differential monitors driveshaft rotation The ABS computer examines changes in shaft speed to predict rear wheel lock up Both rear brakes are operated by a single hydraulic channel The ABS computer controls rear hydraulic performance when necessary using a single channel Hydraulic Control Modulator described later e 3 Channel This
113. led the Assembly Line Commu nication Link ALCL or simply test connector e The connector is located under the dashboard on the driver s side e The connector may be in full view or it may be recessed behind a panel An opening in the panel allows access to recessed connectors e The connector may have a slip on cover labeled Diagnostic Connec tor Remove cover for testing Replace cover after testing Some vehicles require this cover in place for proper operation 5 Verify Ignition Key is OFF 6 Put TEST switch on ABS e 7 Plug the Code Scanner into the Test Connector e The Code Scanner only fits ONE WAY into the test connector e The Code Scanner will not harm the vehicle engine computer Note The Code Scanner does not use all of the test connector contacts Also one Code Scanner pin may plug into an empty test connector position This is normal 8 Turn Ignition Key to ON Position but DO NOT START THE ENGINE WARNING Stay away from the radiator cooling fan It may turn on 9 Get a Trouble Code from Flashing Anti Lock Light e All codes are two 2 digits long e Count flashes to get trouble codes Flashes start after about a 4 second delay The first digit is flashed then there is a 3 second pause then the second digit is flashed then the anti lock light turns ON and stays ON Do not count this steady light as
114. lternator and voltage regulator are working properly Make sure vehicle battery is fully charged Make sure all ABS fuses fusible links and relays are good e Inspect wiring for Contact with sharp edges This happens often Contact with hot surfaces such as exhaust manifolds Pinched burned or chafed insulation Proper routing and connections e Check electrical connectors for Corrosion on pins Bent or damaged pins Contacts not properly seated in housing Bad wire crimps to terminals Problems with electrical connectors are common Inspect carefully Note that some connectors use a special grease on the contacts to prevent corrosion Do not wipe off Obtain extra grease if needed from your vehicle dealer Itis a special type for this purpose Make sure any recommended system flushing has been per formed Corrosion or dirt in ABS valving can result in poor pedal performance Some body and chassis work procedures can harm the ABS computer Disconnect vehicle computer modules when using electric welding equipment Do not expose the ABS computer to high heat for a long time for example during vehicle painting Keeping temperature below 185 F 85 C for less than 2 hours is usually safe 48 READING CODES How to Use the Code Scanner to Read ABS Codes 1 Use the chart to find the ABS system used on your vehicle 2 Refer to the page listed w
115. lutch in the transmission torque convertor When activated the lock up clutch directly connects the engine to the transmission During warm engine cruise conditions the ECM energizes this solenoid to eliminate transmission slippage and increase fuel economy The ECM releases the lock up action when driving conditions require the transmission to operate as normal TDC Top Dead Center When a piston is at its uppermost position in the cylinder maximum compression Thermistor A resistor whose resistance changes with temperature Thermistors are used as sensors for vehicle coolant and manifold air temperature The resistance decreases as temperature goes up TPS Throttle Position Sensor This is a rotary type potentiometer connected 39 to the throttle shaft It has a voltage signal output which increases as the the throttle is opened This sensor is used by the ECM for idle speed spark advance fuel delivery emission system and automatic transmission electronic type control TTS Transmission Temperature sensor This sensor is a thermistor a resistor whose resistance decreases as temperature rises It is mounted within the transmission housing The ECM uses this sensor to monitor transmission operating temperature VSS Vehicle Speed Sensor This sensor sends a frequency signal to the ECM The frequency increases as the vehicle moves faster to give the ECM vehicle speed information
116. n by measuring how fast pulses appear Hall Effect type sensors may be used to measure speed and position of the crankshaft or camshaft for spark timing or fuel injector control 36 Handwheel sensor This is a three wire sensor power ground and signal wires It is used in some Variable Assist Power Steering systems The ECM uses the sensor signal to determine how fast the steering wheel is being turned Then the ECM can apply the correct amount of power steering assist based on vehicle speed See EVO Electronic Variable Orifice actuator definition for more information HEI High Energy Ignition Ignition system which pulses the spark coil by using transistor switches instead of mechanical breaker points The electronics are in a module which use a reference signal coming from a magnetic pick up coil driven by the camshaft Hertz Hz A term for frequency cycles per second IAC Idle Air Control This is a device mounted on the throttle body It adjusts the amount of air bypassing a closed throttle so that the ECM can control idle speed The IAC isa stepper motor which moves a pintle within the air bypass passage When the ECM wants to change idle speed it will move the pintle backwards for more air and faster idle or it will move it forward for less air and slower idle See Stepper Motor definition Idle switch This is a switch built into the tip of the ISC Idle Speed Control
117. nd sometimes at idle the sensor will be too cool to operate no signal sent The computer must operate open loop during this time because it cannot use the sensor to check the air fuel ratio Acceleration deceleration and idle conditions As long as the engine and oxygen sensor are hot the computer can operate closed loop for best economy and least emissions During the drive conditions listed on the left the computer may have to ignore the sensor and run open loop relying on internal programming for fuel delivery instruc tions During idle for example the oxygen sensor may cool down and stop sending a signal A different situation can occur during wide open throttle acceleration The computer sometimes adds additional fuel on purpose for temporary acceleration power The computer knows it is running rich so it ignores the sensor signal until the wide open throttle condition is over How the computer controls idle speed Throttle position and RPM sensors tell the computer when the vehicle is idling Sometimes an idle position switch on the throttle is used The computer simply watches RPM and adjusts an idle speed control device on the vehicle to maintain the desired idle condition Note that this is another example of closed loop operation The computer performs an action activating an idle control device then watches the results of its action engine RPM and readjusts as necessary un
118. nel opening e The connector may have a slip on cover labeled Diagnostic Connector Remove cover for testing Replace cover after testing Some vehicles require this cover in place for proper operation 4 Verify Ignition Key is OFF 5 Put the TEST switch on ABS 6 Plug the Code Scanner into the test the test connector e The Code Scanner only fits ONE WAY into the test connector e The Code Scanner will not harm the vehicle computer Note The Code Scanner does not use all of the test connector contacts This is normal 7 Turn Ignition Key to ON Position but DO NOT START THE ENGINE WARNING Stay away from the radiator cooling fan It may turn on 8 Get Codes from the Flashing Anti Lock Light e Count flashes to get trouble codes Flashes begin after a few seconds Code 12 looks like ale al gt Av PAUSE ZETA FLASH pause FLASH FLASH FLASH 1 FLASH FLASH 2 Put 1 and 2 together code 12 Code 23 looks like WN NUNN AN AN PAUSE IO ASTIN FLASH FLASH pause FLASH FLASH FLASH e Each code is flashed three 3 times before the next trouble code is sent e After all codes are sent the whole sequence is repeated This continues until the ignition key is turned OFF so you can double check your code list Example of code 12 only ale ale als Av PAUSE JETA FLASH pause FLASH FLASH longer pause als D SE Av P
119. ng trouble codes to help pinpoint the problem IMPORTANT Always follow vehicle service manual proce dures for any ABS repairs Erasing ABS Codes from Computer Memory Bosch 2U Version B Erase codes from memory whenever you complete a repair or to see if a problem will occur again Note The computer will automatically erase codes after several restarts typically 100 if the problem does nat return Proceed as follows 1 Turn the ignition switch to the ON position The anti lock lamp should e turn OFF after 3 to 4 seconds If it does not a current failure still exists which must be corrected before its corresponding trouble code will clear 2 Plug the Code Scanner make sure the TEST switch is in the ABS position into the test connector until the anti lock lamp turns ON Remove the Code Scanner The anti lock lamp will turn OFF Si a 3 Withoutturning the ignition switch OFF repeat the sequence outlined in Step 2 2 more times 4 All diagnostic trouble codes should now be cleared Confirm this by turning the ignition switch OFF installing the Code Scanner and turning the ignition switch back to the ON position do not start the engine Code 12 the diagnostic system operational code should be the only code displayed 5 Turn the ignition switch OFF Remove the Code Scanner and reinstall the test connector cover if used on vehicle ABS Code M
120. ng one injector for each cylinder The injectors are mounted in the intake manifold The injectors are fired in groups rather than individually Open circuit A break in the continuity of a circuit such that no current can flow 37 Open Loop O L This is when the control system performs an action expecting a certain result but has no way of verifying if the desired results were achieved Example the ECM operates a fuel injector expecting a certain amount of fuel to be delivered The ECM assumes everything in the fuel system is performing as expected In open loop operation the ECM has no way of checking the actual amount of fuel delivered Thus a faulty fuel injector or incorrect fuel pressure can change the amount of fuel delivered and the ECM would not know it In general a control system operates open loop only when there is no practical way to monitor the results of an action Example Fuel delivery during cold engine warm up The computer runs open loop because the oxygen sensor is not ready to send a signal Without the sensor signal the computer can not check the actual amount of fuel delivered O Oxygen sensor The oxygen sensor is threaded into the exhaust manifold directly into the stream of the exhaust gases The ECM uses the sensor to fine tune fuel delivery The sensor generates a voltage of 0 6 to 1 1 volts when the exhaust gas is rich low oxygen content
121. ng or fuel injector control Driveshaft vehicle speed transmission or torque convertor control cooling fan use variable assist power steering and cruise control Wheel Speed anti lock brake or traction control systems Sensor Device which give the ECM information The ECM can only work with electrical signals The job of the sensor is to take something the ECM needs to know such as engine tempera 38 ture and convert it to an electrical signal which the ECM can understand The ECM uses sensors to measure such things as throttle position coolant temperature engine speed incoming air and the like SFI or SEFI Sequential Fuel Injection or Sequential Electronic Fuel Injection A fuel injection system using one injector for each cylinder The injectors are mounted in the intake manifold The injectors are fired individually in the same sequence as the spark plug firing sequence Shift solenoid Used in computer controlled transmissions The solenoids usually two are located in the transmission housing and are controlled by the ECM The ECM energizes the solenoids individually or in combination to select a specific gear The solenoids control the flow of hydraulic fluid to the transmission shifting valves The ECM selects the appropriate gear ratio and shift point based upon engine operating conditions Short circuit A fault condition an unwanted connection of one el
122. ning lean Various mechanical electronic or wiring problems can cause the computer to sense a rich or lean running engine Usually these conditions will generate a trouble code such as 44 lean exhaust or 45 rich exhaust Follow vehicle service manual troubleshooting charts to find the cause The Field Service Test lets you check to see if the problem was fixed Light flashing equally ON and OFF once a second Note While in the Field Service Mode New trouble codes are not stored in computer memory On some engines the computer will send a signal for a fixed spark advance 5 Turn Ignition Key OFF e Remove Code Scanner and re install connector cover if supplied e The computer system is now back to normal e This completes the Field Service Test COMPUTER BASICS What does the Engine Control Computer do This section further explains the engine computer control system the types of sensors and how the computer controls fuel delivery idle speed and timing The following is an introduction to computer controlled engine systems Additional information may be found in books dealing with this subject available at your local library or auto parts store The more you know about the computer system the better and faster you can troubleshoot and fix problems Why Computers Computer controls were installed in vehicles to meet Federal Government regulations
123. nt condition in subject circuit SYSTEM 6 Teves Mark II Version B 1989 Eldorado Reatta Riviera Seville Toronado 1990 Eldorado Reatta Riviera Seville Toronado Trofeo Pre Diagnostic Visual Inspection Complete all steps before reading trouble codes 1 Check brake fluid level 2 Release the parking brake if it is set 3 Check all ABS system fuses 4 Check system electrical connections Wheel speed sensor connectors EBCM Electronic Brake Control Module connectors System relay connectors System grounds This completes the visual inspection Perform FUNCTIONAL CHECK before reading codes Functional Check 1 Turn the ignition key to the ON position but do not start the dee engine 2 The anti lock lamp should illuminate for at least 3 seconds If it does not refer to the proper diagnostic chart in the vehicle service manual 3 Observe the anti lock and brake lamps while starting the engine ignition key is in the cranking position Both the anti lock and brake lamps should be ON during cranking If they are not refer to the proper diagnostic chart in the vehicle service manual 4 When the engine starts allow it to run for 30 seconds and then turn it OFF for 10 seconds 5 Return the ignition key to the ON position do not start the engine and wait 10 seconds Observe the condition of the anti lock and brake warning lamps If the anti lock
124. ntrol the lock up clutch in an automatic transmission torque convertor The clutch is locked during steady warm engine cruise conditions This improves fuel economy by eliminating power loss in the torque convertor The computer energizes a solenoid to achieve lock up Signals from the engine coolant temperature throttle position and vehicle speed sensors are used e Transmission Control Some transmissions have computer controlled shifting Two solenoids mounted in the transmission are energized singly or in combination to select a gear ratio The solenoids direct the flow of fluid within the transmission to cause the shift The computer uses throttle position 32 vehicle speed engine loading and other sensor information to determine the optimum shift performance The computer can also set the shift quality anywhere from harsh to smooth This is done using a force motor actuator in the transmission to adjust the internal fluid line pressure More information The Glossary Section 8 describes various sensors and actuators used in computer controlled engine systems You can learn more by reading these definitions GLOSSARY A C Air conditioner A C Clutch relay The ECM uses this relay to energize the A C clutch to turn the A C system on or off A C On A C Signal An input signal to the ECM indicating that either the A C compressor is running or that A C operation is being requested
125. o the intake manifold The canister collects vapors evaporating from the fuel tank preventing them from escaping into the atmosphere and causing pollution During warm engine cruise conditions the ECM energizes the Purge solenoid so the trapped vapors are drawn into the engine and burned Quad Driver An electrical device inside the ECM It functions as four separate electronic switches allowing the ECM to energize relays or solenoids Relay A mechanical device for switching high current circuits on and off It is electronically controlled by a low current circuit Relays allows a low power ECM signal to control a high power device such as an electric cooling fan Reluctance sensor This sensor type consists of a permanent magnet with a coil of wire wrapped around it Nearby the sensor is a toothed reluctor ring made of iron or steel The ring is attached around a rotating component such as the crankshaft Whenever a tooth from the ring passes by the sensor it attracts the magnetic field lines surrounding the magnet As the field lines move they pass through the wire coil which generates a small voltage pulse magnetic induction principle Thus a voltage pulse is generated every time a tooth passes by the sensor coil The ECM determines the speed of rotation by measuring how fast pulses appear Reluctance sensors may be used for Crankshaft or Camshaft speed position spark timi
126. oblem with its associated wiring 11 ECM Electronic Control Module Failure This code indicates an anti lock brake system control module failure or a mis read code 12 ECM Electronic Control Module Failure This code indicates an anti lock brake system control module failure or a mis read code 13 ECM Electronic Control Module Failure This code indicates an anti lock brake system control module failure 14 ECM Electronic Control Module Failure This code indicates an anti lock brake system control module failure 15 ECM Electronic Control Module Failure This code indicates an anti lock brake system control module failure SYSTEM 8 Kelsey Hayes AWAL 4 Wheel Anti Lock 1990 1991 1992 1993 1994 Astro Safari Astro Bravada S 4 T Series Blazer Jimmy Pickup Safari Sonoma Syclone Typhoon Astro Bravada C amp K Series Blazer amp Pickup S T Series Blazer Jimmy Pickup Safari Sierra Sonoma Suburban Syclone Typhoon Yukon Astro Bravada C amp K Series Blazer amp Pickup G Series Van S T Series Blazer Jimmy Pickup Safari Sierra Sonoma Suburban Syclone Typhoon Yukon Astro Bravada C amp K Series Blazer amp Pickup G Series Van S amp T Series Blazer Jimmy Pickup Safari Sierra Sonoma Suburban Yukon Diagnostic Circuit Check diagnostic procedure outlined in Complete all steps before reading trouble codes your vehicle ser
127. ont outlet valve solenoid and its circuitry 26 Rear Inlet Valve Checks for open shorted or intermittent condition in the rear inlet valve solenoid and its circuitry 27 Rear Outlet Valve Checks for open shorted or intermittent condition in the rear outlet valve solenoid and its circuitry 31 Left Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 32 Right Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 33 Right Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 34 Left Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 35 Left Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 36 Right Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 37 Right Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 38 Left Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 84 41 Left Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 42 Right Front Wheel Speed Sensor circuit Checks for an open sh
128. ontrol or duty cycle solenoid on electronic controlled carburetors that everything is working the way it should Sensor used exhaust gas oxygen sensor Note Not all engines use every sensor listed above Cold engine warm up condition An example of Open Loop opera tion The coolant temperature sensor tells the computer how warm the engine is Factory engineers know what the best air fuel mixture is for the engine at various operating temperatures More fuel is needed for a cold engine This information is permanently pro grammed into the computer After the computer knows the engine tempera ture it determines the amount of air coming in then it will look at its programming to find out how much fuel to deliver and operate the fuel injectors accordingly Engines with electronic carburetors don t do any of this They have a thermostatically controlled choke just like non computer engines This process is an example of Open Loop operation by the computer The control system performs an action expecting a certain result but has no way of verifying if the desired results were achieved In this case the computer operates a fuel injector 29 expecting a certain amount of fuel to be delivered The computer assumes everything in the fuel system is operating as expected In open loop operation the computer has no way of checking the actual amount of fuel delivered Thus a faulty fuel
129. ontrol Module connectors are properly installed not loose 4 Check that the parking brake switch is functioning properly 5 Check that the brake pressure modulator valve ground stud is clean and tight This completes the visual inspection Perform FUNCTIONAL CHECK before reading codes Functional Check DeVille Eldorado Seville 1 Start the engine The anti lock lamp should come ON during engine cranking and turn OFF shortly after the engine starts If The lamp does NOT turn OFF after engine start or The ANTILOCK DISABLED message appears or The TRACTION DISABLED message appears then proceed to READING ABS CODES page 71 Reading ABS Codes Bosch 2U Version C IMPORTANT Perform all steps in PRE DIAGNOSTIC VISUAL INSPEC TION and FUNCTIONAL CHECK before reading ABS codes 1 Take Safety Precautions e Set parking brake block drive wheels e Put shift lever in PARK automatic transmission or NEUTRAL manual transmission e Make sure ignition key is in OFF position 2 Have a Pencil and Paper Ready This is for writing down all the codes 3 Find the Computer Test Connector e Service manuals call this connector the Assembly Line Diagnostic Link ALDL connector It may also be called the Assembly Line Communi cation Link ALCL or simply test connector e The connector is located under the dashboard on the driver s side e The connector may be
130. or OR Secondary air injection system circuit problems 31 Manifold absolute pressure MAP sensor signal voltage is low OR Fuel injector OR Park Neutral switch circuit problems OR CAM sensor circuit problems OR Engine speed control governor malfunction Van OR Turbocharger wastegate overboost OR Wastegate electrical signal open or shorted to ground OR Purge solenoid voltage high carburetor engines 32 Barometric pressure BARO sensor circuit failure OR Exhaust gas recirculation EGR valve diagnostic switch closed during engine start up or open when EGR flow requested by ECM OR EGR EVRV 33 Mass air flow MAF sensor signal voltage or frequency is high during engine idle OR Manifold absolute pressure MAP sensor signal voltage is high during engine idle Note Engine mis fire or unstable idle may cause this code 17 34 Mass air flow MAF sensor signal voltage or frequency is low during engine cruise OR Manifold absolute pressure MAP sensor signal voltage is low during ignition on OR Pressure sensor circuit signal voltage too high or low carburetor engines 35 Idle air control IAC system problem can not set desired RPM 36 Mass air flow MAF sensor burn off circuit problem OR Transmission shift problem electronically controlled transmissions only OR Direct ignition system DIS
131. or short circuit problems 85 Electronic control module ECM computer circuit problems faulty programmable read only memory PROM OR Transmission Input or output speed sensor circuit problems Speed sensor signals do not agree with with selected gear range OR Torque converter clutch TCC TCC is mechanically stuck on 86 Electronic control module ECM computer circuit problems faulty analog to digital A D converter OR Transmission Low gear error transmission in 3rd or 4th gear when computer commanding 1st or 2nd gear 87 Electronic control module ECM computer circuit problems faulty electrically erasable programmable read only memory EEPROM OR Transmission High gear error transmission in 1st or 2nd gear when computer commanding 3rd or 4th gear 20 Electronic control module ECM computer circuit problem internal reset occurred 91 Skip shift light open or short circuit problems in skip shift light circuit 93 Pressure control solenoid transmission line pressure not at desired level 95 Change oil light wrong voltage is present in light circuit for more than 26 seconds 96 Transmission voltage low low system voltage possibly caused by generator voltage supply circuit or power train control module PCM OR Low oil light wrong voltage is present in light circuit for more than 26 seconds 97 Vehicle speed sen
132. ort or intermittent condition in subject circuit 43 Right Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 44 Left Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circui 45 Left Front Wheel and One 1 Rear Wheel Speed Sensor Signal Missing Checks for missing signal in the subject circuits 46 Right Front Wheel and One 1 Rear Wheel Speed Sensor Signal Missing Checks for missing signal in the subject circuits 47 Either Rear Wheel Speed Sensor Signal Missing Checks for missing signal in either of the rear wheel speed sensor circuits Note that it is impossible to determine which of the rear wheel speed circuits is causing the problem This code will set if the front wheels spin while the rear wheels are stationary 48 Any three Wheel Speed Sensor Signals Missing There are missing signals in three 3 of the four 4 wheel speed sensor circuits 51 Left Front Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 71 which has the same meaning 52 Right Front Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pressure reduction
133. osion etc 41 Right Front Isolation Valve Solenoid open circuit Double check to make sure that the code has been properly read If it has clear all trouble codes by following the ERASING ABS CODES FROM COMPUTER MEMORY procedure on page 88 Thoroughly road test the vehicle Check for trouble codes again If this code returns the EHCU Electro Hydraulic Control Unit is defective and should be replaced The EHCU is a costly part Your dealer may offer an exchange policy in which case your defective unit has value core credit towards the purchase of the replacement Securely attach a tag to your defective unit clearly indicating the trouble code s reported by the defective EHCU 42 Right Front Pulse Width Modulation Valve Solenoid open circuit Refer to the explanation under trouble code 41 43 Right Front Isolation Valve Solenoid short circuit Double check to make sure that the code has been properly read Carefully check all power and ground connections at the EHCU If the code has been properly read and there are no problems in the power or ground circuits clear all trouble codes by following the ERASING ABS CODES FROM COMPUTER MEMORY procedure on page 88 Thoroughly road test the vehicle Check for trouble codes again If this code returns the EHCU Electro Hydraulic Control Unit is defective and should be replaced The EHCU is a costly part Your dealer may offer an exchange policy in whic
134. position of the subject valve does not match the commanded position as given by the EBCM Electronic Brake Control Module 55 Rear Wheel Solenoid Valve circuit This code will set if the physical position of the subject 57 valve does not match the commanded position as given by the EBCM Electronic Brake Control Module 61 Pump Motor or Motor Relay circuit This code will set if the position of the motor relay contacts do not match the commanded position of those contacts as given by the EBCM Electronic Brake Control Module There is a motor monitoring circuit in the EBCM which will detect a defective relay or pump motor 63 Solenoid Valve Relay circuit This code will set if the position of the valve relay contacts do not match the commanded position of those contacts as given by the EBCM Electronic Brake Control Module There is a motor monitoring circuit in the EBCM which will detect a defective relay or a failure in the associated circuitry 71 EBCM Electronic Brake Control Module failure This code will set if there is an internal failure of the Electronic Brake Control Module 75 Lateral Accelerometer circuit This code will set if there is a short or open circuit problem in the associated circuitry 76 Lateral Accelerometer signal error This code will set if the accelerometer signal indicates greater than 0 6g for 2 minutes or more SYSTEM 2 Bosch 2U Version A 1
135. r adjusts timing according to factory programmed instructions Some vehicles have a knock sensor The computer can fine tune the spark timing if this sensor signals an engine knock condition A timing signal EST Electronic Spark Timing is sent by the computer to an ignition module which eventually creates the spark The computer uses a crankshaft position sensor to determine piston position so it can send the spark timing EST signal at the proper moment Newer ignition systems use no distributor There are several versions such as Computer Controlled Coil Ignition C31 Direct Ignition System DIS Integrated Direct Ignition IDI and Opti Spark These systems use multiple ignition coils 2 spark plugs are wired to each coil Sensors for crankshaft position or camshaft position or both are used by both the ignition module and computer to fire the correct coil at the proper time The computer provides spark advance timing as before by looking at vehicle speed engine load and temperature RPM throttle position coolant temperature and manifold pressure or mass air flow sensors are used Refer to vehicle service manual for detailed ignition system descriptions Computer controlled emission systems e EGR Exhaust Gas Recirculation Valve The EGR valve lets exhaust gases re enter the intake manifold and mix with the incoming air fuel The presence of exhaust gases reduces combustion temperatur
136. r intermittent condition in subject circuit Vehicle speed must be equal to or greater than 4 MPH for this code to set 36 Left Rear Toothed Wheel Frequency Error Checks for excessively dirty or damaged toothed wheel sensor ring Mis matched tire sizes or use of the temporary mini spare tire may set this code 41 Right Front Solenoid Valve circuit This code will set if the physical position of the subject valve does not match the commanded position as given by the EBCM Electronic Brake Control Module 45 Left Front Solenoid Valve circuit This code will set if the physical position of the subject valve does not match the commanded position as given by the EBCM Electronic Brake Control Module 69 55 Rear Axle Solenoid Valve circuit This code will set if the physical position of the subject valve does not match the commanded position as given by the EBCM Electronic Brake Control Module 61 Pump Motor or Motor Relay circuit This code will set if the position of the motor relay contacts do not match the commanded position of those contacts as given by the EBCM Electronic Brake Control Module There is a motor monitoring circuit in the EBCM which will detect a defective relay or pump motor 63 Solenoid Valve Relay circuit This code will set if the position of the valve relay contacts do not match the commanded position of those contacts as given by the EBCM Electronic Brak
137. r Memory Teves Mark II Version B Erase codes from memory whenever you complete a repair or to see if a problem will occur again 1 IMPORTANT Trouble codes cannot be cleared until they have been read Referto READING ABS CODES page 82 2 Drive the vehicle at a speed of greaterthan 20 MPH Trouble codes should automatically clear ABS Code Meanings Teves Mark II Version B IMPORTANT Always follow vehicle service manual procedures for any ABS repairs 11 EBCM Electronic Brake Control Module Failure In most cases this code indicates an EBCM failure Follow the appropriate chart to check the ground circuit 12 EBCM Electronic Brake Control Module Failure In most cases this code indicates an EBCM failure Follow the appropriate chart to check the ground circuit 21 Main Valve Checks for open shorted or intermittent condition in the main valve solenoid and its Circuitry 22 Left Front Inlet Valve Checks for open shorted or intermittent condition in the left front inlet valve solenoid and its circuitry 23 Left Front Outlet Valve Checks for open shorted or intermittent condition in the left front outlet valve solenoid and its circuitry 24 Right Front Inlet Valve Checks for open shorted or intermittent condition in the right front inlet valve solenoid and its circuitry 25 Right Front Outlet Valve Checks for open shorted or intermittent condition in the right fr
138. ra 1994 Blazer C 4 K Series Pickup Truck S 8 T Series Pickup Truck Diagnostic Circuit Check Complete all steps before reading trouble codes 1 Block the wheels and release the parking brake Do not step on the service brake 2 Turn the ignition key to the ON position but do not start the engine Observe the instrument panel brake warning light e If the brake light turns ON and then OFF after about 2 seconds the self diagnostic circuitry has found NO current problems with the ABS system DO NOT perform ABS code reading procedure A false code 9 will be stored in ABS computer memory if the code reading steps are followed when no faults currently exist This is a quirk of the RWAL ABS system Do this additional check Step on the service brake If the brake warning light comes ON there is a problem with the combination valve This valve is part of the normal braking system not part of the anti lock braking system Release the service brake If the brake light turns ON and stays ON or turns ON after the bulb check proceed to the diagnostic procedure outlined in your vehicle service manual for the brake light ON symptom If the brake light stays OFF proceed to the diagnostic proce dure outlined in your vehicle service manual for the brake light OFF symptom e If the brake light is FLASHING proceed to READING ABS CODES page 87 3 Turn the ignition key to the OFF position
139. rouble codes 1 Check that all ABS system grounds are clean and tight e 1991 Brougham Eldorado Reatta Riviera Seville Toronado Trofeo Check the ground that is located behind the right headlight Check the ground that is located near the parking brake pedal on the left side of the dash e 1992 Eldorado Seville Check the ground that is located on the engine near the alternator Check the ground that is located on the rear seat brace e 1992 Riviera Toronado Trofeo Check the ground that is located behind the right headlight Check the ground that is located in the right front engine compart ment e 1993 Riviera Check the ground that is located behind the right headlight Check the ground that is located on top of the left shroud 2 Check power sources which supply various parts of ABS system e 1991 Brougham Check the GA TRANS fuse in the underdash fuse block Check the ABS fuse in the underdash fuse block Check the rust colored fusible link E on the positive junction block e 1991 Eldorado Seville Check fuse number 7 in the interior relay center Check the black and blue colored fusible links on the positive junction block e 1991 Reatta Riviera Check fuse number 4 in the interior relay center Check the black and blue colored fusible links on the positive junction block e 1991 Toronado Trofeo Check fuse number
140. rs may be used depending upon the engine vehicle type or other tasks the computer must do Note that information from one sensor may be used by the computer for many different tasks For example engine temperature is something the computer needs to know when controlling fuel delivery spark timing idle speed and emission systems The sensor information may be very important for one engine control function but only used to fine tune a second one There are several types of sensors e Thermistor This is a resistor whose resistance changes with temperature It is used to measure temperatures of coolant or incoming air It has two wires connected to it e Potentiometer This signals a position such as throttle position or EGR valve position It connects to three wires one for power one for ground and one to carry the position signal back to the computer e Switches These are either ON voltage signal to the computer or OFF no voltage signal to the computer Switches connect to two wires and tell the computer simple things such as whether or not the air conditioner is running e Signal Generator These create their own signal to tell the computer of some condition such as exhaust gas oxygen content camshaft position or intake manifold vacuum They may have one two or three wires connected to them The computer controls things with actuators The computer can only send out electrical signals
141. s in this circuit 36 Left Rear Wheel Speed Sensor Voltage Output is incorrect This code indicates a problem in the wheel speed sensor or its associated tone toothed wheel Check for the proper air gap between the wheel speed sensor and tone wheel missing or broken teeth on the tone wheel a loose improperly mounted or mis adjusted wheel speed sensor An intermittent connection in the associated wiring can also set this code 37 Left Rear Wheel Speed Sensor Voltage Output is erratic Erratic voltage output usually indicates a loose dirty or corroded connection Check the connections at the wheel speed sensor connector the wheel speed sensor harness and the EHCU Electro Hydraulic Control Unit There may also be a problem in the wheel speed sensor or its associated tone toothed wheel Check for the proper air gap between the wheel speed sensor and tone wheel missing or broken teeth on the tone wheel a loose improperly mounted or mis adjusted wheel speed sensor 38 Speed Sensor Voltage Signal Output is erratic When this code appears it is 94 usually accompanied with code 23 27 33 or 37 If it is accompanied with one or more of the listed codes use the trouble chart for that code to diagnose the system If trouble code 38 appears by itself all connections between the wheel speed sensors and the EHCU Electro Hydraulic Control Unit will need to be checked for looseness dirt corr
142. s the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 73 which has the same meaning 54 Left Rear Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM Electronic Brake Control Module Note This code may also be sent along with Code 74 which has the same meaning 55 Left Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 56 Right Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 57 Right Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 58 Left Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 61 Shorted Low Fluid or Hydraulic Pressure Switch or shorted ABS diode or associated circuitry This code will set if the low fluid switch the hydraulic pressure switch or the ABS diode or any of the associated circuitry exhibits a short circuit condition 71 Left Front Wheel Hydraulic Pressure Reduction fault This code is the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM El
143. sor VSS output circuit problems 99 Tachometer output circuit problems Saturn Transmission Codes GM Saturn engine codes and GM transmission code list begins on page 16 Note Code numbers labeled Information Flag may be sent along with the regular unlabeled trouble codes The computer sends Information Flags to help you find the cause of a trouble code Note that conditions which only cause an Information Flag will not turn on the Check Engine light Refer to vehicle service manual troubleshooting charts 13 Information Flag Line pressure high 14 Information Flag Line pressure low 15 Information Flag Hot light 16 No 1st gear OR Information Flag Electrical variable orifice EVO fault 18 Information Flag No gears available 21 2nd gear stuck on 22 No 2nd gear 23 No 3rd gear 24 No 4th gear 25 No torque converter clutch 26 Torque converter clutch stuck on 27 Information Flag Quick quad driver output fault open or short circuit on any of the qaud driver module circuits ADM that lasts 5 seconds or longer 31 Transaxle temperature circuit open 32 Transaxle temperature circuit grounded 34 Information Flag Powertrain Control Module PCM computer circuit problem communications failure 35 No turbine speed signal 36 Turbine speed signal noise 41 Vehicle Speed Sensor
144. sor measures the amount of air entering the engine and sends a frequency or voltage signal depends upon sensor type to the ECM The signal voltage or frequency increases when the amount of incoming air goes up This gives the ECM information required for control of fuel delivery and spark advance MAP Manifold Absolute Pressure sensor This sensor measures manifold vacuum and sends a frequency or voltage signal depends upon sensor type to the ECM This gives the ECM information on engine load for control of fuel delivery spark advance and EGR flow MAT Manifold Air Temperature sensor This sensor is a thermistor a resistor whose resistance decreases with temperature It is threaded into the intake manifold so the ECM can determine the temperature of the incoming air This is used for fuel delivery calculations MCS Mixture Control Solenoid Used on computer controlled vehicles having carburetors Built into the carburetor it allows the ECM to fine tune fuel delivery during warm engine cruise MEMCAL A small electronic assembly containing the the functions of both the PROM and CALPAK It is hidden behind an access door on the ECM and is replaceable Only some ECM s have MEMCAL MFI Multi Port Fuel Injection See MPFI definition Mode A type of operating condition such as idle mode or cruise mode MPFI Multi Port Fuel Injection A fuel injection system usi
145. st connector cover if used on vehicle e 1992 and newer 1 Turn the ignition switch to the ON position 2 Put the Code Scanner TEST switch in the ABS position 3 Plug the Code Scanner into the test connector for 2 seconds Remove the Code Scanner for 1 second Repeat this procedure once more Trouble codes are erased when the anti lock and brake lights turn on then turn off Repeat the plug unplug procedure if necessary 4 Turn the ignition switch to the OFF position Reinstall test connector cover if used on vehicle ABS Code Meanings Kelsey Hayes 4WAL IMPORTANT Always follow vehicle service manual procedures for any ABS repairs 12 ABS System functional 2WD service brake not applied This code indicates that the anti lock brake system as installed on a 2 wheel drive vehicle is functioning normally As indicated above this code should appear without the service brakes applied 13 ABS System functional 2WD service brake applied This code indicates that the anti lock brake system as installed on a 2 wheel drive vehicle is functioning normally As indicated above this code should appear with the service brakes applied If with the service brakes applied the anti lock lamp continues to indicate a code 12 it is likely that there is a problem with the stop brake lamp switch circuit Assistance is available under the diagnostic chart for diagnostic trouble code 81
146. te of engine run Left sensor on dual sensor engines 46 Vehicle anti theft system VATS failure OR Power steering pressure switch failure 47 Electronic control module ECM computer circuit problems universal asynchronous receiver transmitter UART link or data loss OR Knock sensor module located in the computer is not working properly 48 Misfire symptom OR Mass air flow MAF sensor open or short circuit MAF sensor signal 49 High idle RPM or vacuum leak Saturn 51 Electronic control module ECM computer circuit problems faulty programmable read only memory PROM MEM CAL ECM or checksum errors 52 Electronic control module ECM computer circuit problems faulty or missing CALPAC or MEM CAL analog to digital converter A D error or Quad Driver module QDM fault OR Oil temperature sensor signal voltage is low Corvette OR System voltage high for a long period of time Electronic transmission note this fault may cause other codes to be set 53 Over voltage condition Electronic transmission note this fault may cause other codes to be set OR Exhaust gas recirculation EGR system problems or EGR Solenoid No 1 problem OR 18 Voltage reference error OR Vehicle anti theft system VATS problems 54 Low fuel pump voltage OR Fuel pump relay OR EGR Solenoid No 2 failure OR Quad Driver module QDM
147. the passenger compartment or close to the ABS hydraulic controller in the engine area The module monitors wheel speed sensors to determine if lock up is about to occur when brakes are applied If so the module will operate the ABS hydraulic solenoids to control brake pressure and prevent lock up This process is described later Refer to How ABS Controls Brakes The EBCM also performs checks of itself and other ABS components during vehicle operation If problems are found the ABS system is disengaged the dashboard warning light is energized and a diagnostic trouble code is stored in ABS computer memory Brake Light Switch This is the usual switch which energizes the rear brake lights when the brake pedal is applied The ABS computer is sometimes connected to this switch depends upon system Note The engine control computer may also be connected to this switch Some ABS systems are active continuously Other types wait for the brake light switch to close before operating Wheel Speed Sensor This is a reluctance sensor a 2 wire type It consists of a permanent magnet with a coil of wire wrapped around it Nearby the sensor is a toothed ring made of iron or steel sometimes called a reluctor sensor ring exciter ring pick up ring or tone Wheel Speed Sensor Operation Magnet Teeth To Wire Coil computer Typical Front Sensor wheel The ring is attached to the wheel drive axle or transmission sh
148. the engine for burning Other computer functions The computer often controls various other functions around the vehicle Detailed explanations may be found in your vehicle service manual Some typical examples are e Air Conditioner A C Clutch The computer can turn off the air conditioner to reduce engine loading This is desirable during heavy acceleration engine cranking or low speed steering maneuvering The computer may also disable the air conditioner when refrigerant pressure is too low or high to prevent A C damage The computer stops the air conditioner by using a relay to disconnect voltage from the A C clutch e Radiator Cooling Fan The computer controls engine cooling fan electric type operation on most vehicles Usually the fan is turned on when engine temperature exceeds a certain level or when the air condition ing system is used The computer uses a relay to power the fan Some vehicles have a second fan for extra cooling e Variable Assist Power Steering Saturn Vehicles This system delivers power steering assist based on vehicle speed little assist during high speed straight steering increased assist for low speed turns The computer controls fluid flow in the power steering pump using an Electronic Variable Orifice EVO actuator more fluid flow provides more steering assist Refer to EVO in Glossary Section 8 for more details e Torque Convertor Clutch The computer can co
149. the warning light Relays Various relays are used by ABS depends upon system Refer to ABS circuit schematics in vehicle service manual Typical relays include e ABS Power relay Supplies power to the electronic brake control module ABS computer Note This relay may have built in diodes to protect the computer against voltage surges or reverse voltage conditions e Electric Pump relay Used by the ABS computer to operate the electric pump This is the pump associated with the accumulator previously described e ABS Solenoid relay Connects vehicle battery voltage to the solenoid circuits in the Hydraulic Control Module Note This does not turn on the solenoids The ABS computer controls individual solenoids by completing each circuit as required Digital Ratio Adapter Controller DRAC This is a small electronic module used on some rear wheel drive vehicles It works with the speed sensor mounted in the differential The DRAC receives the sensor signal processes it then sends it to the ABS computer speedometer and cruise control if installed The DRAC is matched to a specific rear axle ratio and tire size Any change to the rear axle ratio or tire size requires recalibrating or replacing the DRAC Lateral Acceleration Sensor This sensor is only used on Corvette ABS systems It is a small module used to monitor the amount of sideways force exerted on the vehicle during a hard turn The module sends a
150. til the desired idle speed is achieved There are two types of idle speed control devices The first is an adjustable throttle stop that is positioned by a computer controlled motor The second method lets the throttle close completely An air passage bypassing the throttle allows the engine to idle A computer controlled motor adjusts air flow through the bypass to set idle speed Smaller engines can stumble or stall at idle when the air conditioner compressor turns on or the power steering is used To prevent this switches tell the computer when these demands are coming so it can increase the idle accordingly How the computer controls spark advance timing You set spark timing in a non computer engine by using a timing light and adjusting the distributor at idle RPM During vehicle operation timing is changed by either engine vacuum vacuum advance function or by engine RPM centrifugal advance function These spark timing changes are done mechanically inside the distributor Computer controlled vehicles using a distributor still have you set spark timing by using a timing light and adjusting the distributor at idle RPM The timing changes which occur during vehicle operation however are controlled electronically The computer looks at sensors to determine vehicle speed engine load and temperature RPM throttle position coolant temperature and manifold pressure or mass air flow sensors are used Then the compute
151. tion valve to wheel Dump valve is CLOSED not energized This valve has no effect on the brake pressure when it is closed Systems using two stage solenoid Solenoid is not energized Hydraulic flow same as described above The ABS system is capable of repeating the brake cycle at a rapid rate up to 15 times a second Other ABS Uses On some vehicles the components of ABS are shared with another system Anti Slip Regulation ASR also known as traction control This system prevents wheel slip during acceleration on slick road surfaces The ASR system is controlled by a computer module This ASR computer is connected to the same wheel speed sensors and hydraulic control modulator used by ABS If one drive wheel slips excessively during acceleration power will be transferred to the other drive wheel by applying brake pressure to the slipping wheel The ASR computer may try to stiffen throttle movement or retard engine timing before applying brake action ABS SAFETY General Safety Guidelines to Follow When Working on ABS Vehicles WARNING To avoid personal injury DO NOT open a bleeder valve or loosen a hydraulic line while ABS is pressurized Always follow vehicle manufacturer s procedures to depres surize ABS before servicing e Always use specially designed ABS brake hoses and fittings when replacing these parts e Always use ABS recommended brake fluids DO NOT use silicone brake fluids in ABS systems
152. to synchronize spark plug firing Closed Loop C L This is when a control system performs an action expecting a certain result then checks the results and corrects its actions if necessary until the desired results are achieved Example Fuel delivery The ECM operates a fuel injector in a way which should deliver an optimum air fuel mixture if everything in the fuel system is operating as expected In closed loop operation the ECM uses the oxygen sensor to check the results Fuel delivery may be different than expected because of variations in fuel pressure or injector operation If the oxygen sensor indicates a rich condition the ECM will compensate by reducing fuel delivery until the oxygen sensor signals an optimum air fuel ratio Likewise the ECM will compensate for a lean condition by adding fuel until the oxygen sensor once again signals an optimum air fuel mixture Thus closed loop operation means the ECM can fine tune control of a system to get an exact result providing the ECM has a sensor or other means to check results Continuity An unbroken continuous circuit through which an electric current can flow CPS Crankshaft Position Sensor This sensor sends a frequency signal to the ECM It is used to reference fuel injector operation and synchronize spark plug firing on distributorless ignition systems DIS CTS Coolant Temperature Sensor This sensor is
153. trouble codes to help pinpoint the problem IMPORTANT Always follow vehicle service manual procedures for any ABS repairs Erasing ABS Codes from Computer Memory Bosch 2U Version C Erase codes from memory whenever you complete a repair or to see if a problem will occur again Note The computer will automatically erase codes after several restarts typically 100 if the problem does nat return Proceed as follows 1 Turn the ignition N switch to the ON O position The anti lock lamp should rom turn OFF after 3 Kl to 4 seconds If it does not a current failure still exists which must be corrected before its corresponding trouble code will clear 2 Install the Code Scanner make sure the TEST switch is in the ABS position into the test connector until the anti lock lamp turns ON Remove the Code Scanner The anti lock lamp will turn OFF 3 Without turning the ignition switch OFF repeat the sequence outlined in Step 2 2 more times 4 All diagnostic trouble codes should now be cleared Confirm this by turning the ignition switch OFF installing the Code Scanner and turning the ignition switch back to the ON position do not start the engine Code 12 the diagnostic system operational code should be the only code displayed 5 Turn the ignition switch OFF Oy Remove the Code Scanner and reinstall the test connector cover if used on vehicle ABS Cod
154. u can either e Have your vehicle professionally serviced Trouble codes indicate problems found by the computer Or e Repair the vehicle yourself using trouble codes to help pinpoint the problem Trouble Codes and Diagnostics help you fix the problem To find the problem cause yourself you need perform special test procedures called diagnostics These procedures are in the vehicle service manual There are many possible causes for any problem For example suppose you turned on a wall switch in your home and the ceiling light did not turn on Is ita bad bulb or light socket Is the bulb installed correctly Are there problems with the wiring or wall switch Maybe there is no power coming into the house As you can see there are many possible causes The diagnostics written for servicing a particular trouble code take into account all the possibili ties If you follow these procedures you should be able to find the problem causing the code and fix it if you want to do it yourself The Code Scanner makes it easy to fix computer vehicles Using the Code Scanner to obtain trouble codes is fast and easy Trouble codes give you valuable trouble codes are and where they come knowledge whether you go for from you are well on your way to fixing professional vehicle servicing or dont today s computer controlled vehicles yourself Now that you know what When to Read Codes Use the Code Scanner to
155. ulator or Reservoir HYDRAULIC PRESSURE FLOW Isolation valve is CLOSED ener gized Pressure flow between master cylinder and brake caliper cylinder remains blocked because of closed valve Closed isolation valve still prevents changes in master cylinder pressure from reaching wheel caliper cylinder Dump valve is OPEN energized Hydraulic pressure to wheel caliper cylinder is reduced The open dump valve relieves pressure by bleeding some fluid out of the wheel circuit The fluid travels either back to the brake reservoir or to an accumulator depends on system Fluid collected in the accumulator is returned to the master cylinder Some systems use an electric pump to move the fluid Other systems briefly pause the ABS brake cycle Then the spring driven diaphragm inside the accumulator pushes the fluid back to the master cylinder Systems using two stage solenoid Solenoid is fully energized Hydraulic flow same as described above ABS Braking Pressure Increase Wheel speed signals indicate absence of lock up condition ABS computer takes last step in brake control cycle increase hydraulic pressure to wheel caliper cylinder To Wheel Caliper or Cylinder Accumulator or Reservoir HYDRAULIC PRESSURE FLOW Isolation valve is OPEN not energized Master cylinder is reconnected to wheel caliper cylinder Once again hydraulic pressure from master cylinder passes through isola
156. underdash fuse block Check the CLSTR fuse in the underdash fuse block Check rust colored fusible link J on the positive junction block 3 Check that pump motor relay EBCM relay Electronic Brake Control Module solenoid valve relay and EBCM connectors are properly installed not loose This completes the visual inspection Perform FUNCTIONAL CHECK before reading codes Functional Check Corvette 53 1 Start the engine The brake warning lamp should come ON during engine cranking and turn OFF shortly after the engine starts If it does not check the brake warning lamp circuit in accordance with vehicle service manual instructions 2 Turn the engine OFF Turn the ignition key to the ON RUN position but do not start the engine The anti lock lamp should illuminate for about 2 seconds and then turn OFF if no trouble codes are currently stored however history trouble codes may be stored Proceed to Step 3 below If the anti lock lamp stays ON trouble codes are stored Proceed directly to READING ABS CODES page 54 If the anti lock lamp does not turn ON at all or flashes very briefly less than 1 2 of a second a problem exists in the anti lock lamp circuitry See your vehicle service manual 3 Drive the vehicle at least 20 MPH If the anti lock lamp turns ON proceed to READING ABS CODES page 54 Reading ABS Codes Bosch2S IMPORTANT Perform all steps in PRE D
157. valve The second system uses an EGR valve entirely controlled by the ECM This valve contains three individual flow passages small flow medium flow and large flow Each passage has an electric solenoid Passage closed when solenoid off passage open when solenoid energized The ECM energizes one or more solenoids in combination to set up different flow rates through the valve as required The third system is also directly controlled by the ECM This EGR valve is vacuum operated the normally closed valve opens as vacuum is applied The ECM applies control vacuum to the EGR valve using a solenoid connected to a vacuum source The ECM uses a duty cycle type signal to vary the amount of vacuum passing through the solenoid See Duty Cycle definition Electromagnetic Interference Undesired signals interfering with a needed signal For example static on a radio brought about by lightning flashes or closeness to high voltage power lines ESC Electronic Spark Control This is an ignition system function which works on vehicles having a knock sensor mounted on the engine block The knock sensor is wired to circuitry in a separate module early version or inside the ECM later version If the sensor detects engine knock the ESC function alerts the ECM which will immediately retard the 35 spark to eliminate the knock condition EST Electronic Spark Timing An ignition system where the E
158. vice manual for the anti lock light ON symptom e If the anti lock light stays OFF proceed to the diagnostic proce 1 Block the wheels and release the dure outlined in your vehicle parking brake Do not step on the service manual for the anti lock service brake light OFF symptom 2 Turn the ignition key to the ON 3 Turn the ignition position but do not start the engine key to the OFF Observe the instrument panel amber position Proceed anti lock light r to READING e If the anti lock ABS CODES light turns page 91 ON and then OFF after about 2 seconds the diagnostic circuit check is successful Proceed to Step 3 e If the anti lock light turns ON and stays ON or turns ON after the bulb check proceed to the 90 Reading ABS Codes Kelsey Hayes 4WAL IMPORTANT Perform all steps in DIAGNOSTIC CIRCUIT CHECK before reading ABS codes Note 1990 1991 only Codes 21 22 25 26 31 32 35 and 36 will disable ABS system but are not stored in computer memory They are erased when ignition is turned off All other codes are stored in memory when they occur 1 Take Safety Precautions e Set parking brake block drive wheels e Put shift lever in PARK automatic transmission or NEUTRAL manual transmission e Make sure ignition key is in OFF position 2 Have a Pencil and Paper Ready This is for writing down all the codes 3 Find the Computer Test Connector e Service manuals call this
159. voltage low 75 Exhaust gas recirculation EGR system Solenoid No 1 problem OR System voltage low charging system problems OR Transmission voltage low low system voltage possibly caused by generator voltage supply circuit or power train control module PCM 76 Exhaust gas recirculation EGR system Solenoid No 2 problem 17 Exhaust gas recirculation EGR system Solenoid No 3 problem OR Primary cooling fan relay driver circuit circuit problems 78 Secondary cooling fan relay driver circuit circuit problems 79 Vehicle Speed Sensor VSS signal voltage too high OR Transmission Temperature Sensor TTS high temperature indicated 80 Vehicle Speed Sensor VSS signal voltage too low 81 Brake switch circuit problems OR Anti Lock Brake System ABS message fault Saturn OR Transmission Solenoid B 3 2 shift solenoid open or short circuit problems 82 Ignition system fault 3X signal problem OR Electronic control module ECM computer circuit problem internal communications failure Saturn OR Transmission Solenoid A 1 2 shift solenoid open or short circuit problems 83 Torque Converter Clutch TCC solenoid circuit problems OR Reverse Inhibit open or short circuit in reverse inhibit solenoid coil 84 3 2 Control solenoid open or short circuit problems OR Skip shift solenoid open
160. whole sequence is repeated This continues until the ignition key is turned OFF so you can double check your code list e All codes are two 2 digits long 9 Turn Ignition Key OFF 10 Remove Code Scanner and Re install Connector Cover if supplied The computer system is now back to normal operation 11 Refer to ABS Code Meanings on page 93 Kelsey Hayes 4WAL This completes the code reading procedure At this point you can either e Have your vehicle professionally serviced Trouble codes indicate problems found by the computer Or e Repair the vehicle yourself using trouble codes to help pinpoint the problem IMPORTANT Always follow vehicle service manual proce dures for any ABS repairs Erasing ABS Codes from Computer Memory Kelsey Hayes 4WAL Erase codes from memory whenever you complete a repair or to see if a problem will occur again Proceed as follows 1990 1991 Ki 1 Turn the ignition switch to the ON ye 92 position 2 Putthe Code Scanner TEST switch in the ABS position 3 Plug the Code Scanner into the test connector for 2 seconds Remove the Code Scanner for 2 seconds Repeat this procedure 5 more times WK TT Y Li Important A false code 65 may be created if the plug unplug procedure is only done twice You must complete all of step 3 in order to erase trouble codes 4 Turn the ignition switch to the OFF position Reinstall te
161. y 27 Rear Outlet Valve Checks for open shorted or intermittent condition in the rear outlet valve solenoid and its circuitry 31 Left Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 32 Right Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 33 Right Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 34 Left Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 35 Left Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 36 Right Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 37 Right Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 38 Left Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 19 41 Left Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 42 Right Front Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit 43 Right Rear Wheel Speed Sensor circuit Checks for an open short or intermittent condition in subject circuit

CODE SCANNER - Bosch Diagnostics

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