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9 General ABS Service

1. Lower the vehicle Te ay pte v Instructor s Check 450 Job Sheet 26 Name Date Brake System Operation Check Upon completion and review of this job sheet you should be able to complete a thorough oper ational check of the brake system on a vehicle equipped with an ABS ASE Correlation This job sheet is related to the ASE Brakes Test Content Area Anti Lock Brake System ABS Diagnosis and Repair Task Observe ABS warning light s at startup and during road test determine if further diagnosis is needed Tools and Materials Operator s manual or service manual Describe the Vehicle Being Worked On Year Make Model VIN Engine type and size Procedures 1 Ensure parking brake is set 2 Tum ignition to KOEO Observe and record brake warning light s that are lit Compare to specifications in manual Results 3 Start engine and allow to idle Observe and record actions of brake waming light Compare to specifications from manual Results 4 Apply service brakes and release parking brakes Observe and record brake warning light s Results 5 Set parking brakes and switch ignition to off 6 Pump the service brake pedal until the power boost is exhausted Hold the pedal down 7 Start engine Observe and record action s of brake pedal and brake waming lights Results 8 Keep parking brakes applied Apply service brakes Engage either Reverse or Dr
2. 16 REAR SPEED SENSOR CIRCUIT SHORTED 17 INSUFFICIENT PRESSURE IN THE ACCUMULATOR 18 BRAKE LIGHT SWITCH CIRCUIT OPEN 19 VEHICLE SPEED SENSOR CIRCUIT OPEN 20 LOW BRAKE FLUID 1 Antilock brake systems are being discussed Technician A says a code 12 above chart and a lit warming light may cause problems with the regular service brakes Technician B says code 20 above chart and a lit warning light could cause service brake problems Who is correct A A only B B only C Both A and B D Neither A nor B Technician A says a vehicle that experiences vibration in the pedal during panic braking indicates the ABS is functioning properly Technician B says a hard pull to the right during panic stopping with ABS may indicate a wheel alignment problem Who is correct A A only C Both A and B B B only D Neither A nor B Technician A says code 12 above chart and no warning light are probably just indications that the ABS power has been disconnected recently Technician B says a code 16 above chart and a warning light could indicate improper servicing of the differential of a RWAL equipped vehicle Who is correct A A only B B only C Both A and B D Neither A nor B 4 RABS is being discussed Technician A says a code 13 above chart indicates the front sensor probably has a short Technician B says a code 19 may also mean the speedometer is not working Who is correct A A only B B only C Bo
3. store the tools and complete the repair order v Instructor s Check 456
4. turn the ignition off and pump the brake pedal thirty to forty times to exhaust accumulator pressure Leave the ignition off and the accumula tor depressurized while bleeding the brakes You can bleed the system using either manual or pressure bleeding methods as you would a non antilock system The usual bleeding sequence is LR RR LE RF To bleed the master cylinder and hydraulic booster relieve accumulator pressure and top off the reservoir Connect a transparent hose to the bleeder screw on the side of the hydraulic assem bly and place the other end in a clear container filled with a few ounces of brake fluid Open the bleeder screw one half to three quarters tum and tum the ignition on The pump will run and force fluid from the hydraulic assembly into the bleeding container Close the bleeder screw when the fluid flowing into the container is free of air bubbles Disconnect the bleeder hose tum the ignition off and top off the fluid reservoir Bosch 2 2E 2S 2U Micro and ABS ASR You can bleed the Bosch 2 system versions using either manual or pressure bleeding methods generally as you would a non antilock system All of 421 A scan tool isa diagnostic tool that allows the technician to communicate with the vehicle s onboard computers It can be used to command some vehicle actuators to perform certain tasks these Bosch 2 ABS versions have been used by many carmakers for many years Although the basic bleeding proced
5. Front Brake Antilock Sensor LO fee Brake Fluid Level Switch No 2 462 P Pump Motor Speed Sensor Figure 9 8 Part of a pin out chart for testing circuit functions at an ABS control module Courtesy of Ford Motor Company 428 Use Computer Pin Voltage Charts A computer pin voltage or pin out chart identifies all the connector terminals at the main computer connector by number circuit name and function The voltage or resistance levels that should be present under various conditions also are often listed Some circuits have different voltage specifications with the key on and the engine off during cranking and when the engine is running Use the pin voltage charts to check input and output signals at the computer Figure 9 8 is an example of part of a pin out chart for the main connec tor at an ABS control module Checking signals at the computer is closely related to sensor oper ating range tests Check Ground Continuity With the key on circuit energized and current flowing use a digi tal voltmeter to check the voltage drop across the main computer ground connection and across the ground connection of any sensor that you think may be causing a problem Figure 9 9 Low resistance ground connections are critical for electronic control circuits With the ignition on voltage drop across the ground connection for any electronic circuit should be 0 1 volt or less The voltage drop across a high resistance ground connection in seri
6. Remove the bolt that attaches the pump and motor to the hydraulic module 440 Photo Sequence 15 Pump and Motor Removal continued P15 10 Remove the pump and motor assembly by sliding it off the locating pin Wheel Speed Sensor Replacement A problem in a wheel speed sensor may require replacement of the sensor pickup coil and its har ness or the tone ring or both Some wheel sensors have an adjustable air gap between the sensor head and the teeth on the tone ring An equal number of sensors are nonadjustable The sensors shown in Figure 9 14 and Figure 9 15 for example provide no access to either measure or adjust the air gap If a sensor is adjustable follow the carmaker s adjustment procedure exactly Some non adjustable sensors use a lightweight plastic or paper spacer on the mounting surface Figure 9 25 and Figure 9 26 The spacer sets the air gap correctly A new spacer of the correct thickness should be used whenever a sensor is reused Manufacturers differ in their requirements for servicing the wiring harnesses on speed sensors The short two wire hamess that is part of the sensor assembly on GM vehicles is made with very fine wire strands to provide maximum flexibility with minimum circuit resistance GM specifies that the sensor harness should not be repaired by any method If it is damaged the complete sensor assembly must be replaced DaimlerChrysler on the other hand says that the hamesses on most of its whee
7. a trouble code for an open cir cuit fault If a shorted or grounded circuit exists all or almost all of the bias voltage is dropped across the pull up resistor The signal monitor voltage will be lower than the programmed signal monitor voltage Figure 9 22 In this case the computer will immediately set a trouble code for a grounded or shorted circuit The simple voltage divider circuit shown in Figure 9 21 and Figure 9 22 lets the computer detect an electrical fault as soon as the ignition is turned on The wheel does not need to turn even Bias voltage Pull up resistor Signal Open monitor circuit high Pickup coil resistance OPEN Signal circuit monitor HIGH Figure 9 21 If the sensor circuit is open signal monitor voltage will be high 437 Bias voltage Pull up resistor Signal ay monitor low Grounded or Pickup coil shorted resistance circuit GROUNDED or Signal SHORTED monitor LOW circuit Figure 9 22 If the sensor circuit is grounded or shorted signal monitor voltage will be low one revolution You can verify an open or short circuit fault by connecting a voltmeter between the high voltage side of the pickup coil circuit and ground Depending on the circuit fault the meter should read close to full bias voltage or close to zero volts with the ignition on Some speed sensors receive a bias voltage to raise the signal above the common ground plane of the vehicle electric
8. but it does not always pin point the exact cause of the problem Checking DTCs is an overall or area test of the system Carmakers have different names for codes and categorize them in different ways for example 1 GM trouble codes O Ford service codes 4 DaimlerChrysler fault codes With the introduction of the second generation onboard diagnostic systems OBD II for engine control systems in the mid 1990s the term diagnostic trouble code has been widely applied to codes for all automotive control systems Two general terms we can use for all codes are hard codes and soft codes Hard Codes A hard code indicates a failure that is present at the time of testing and perma nent until you fix it If you turn off the ignition and clear the codes a hard code will reappear immediately or within a few minutes because the problem still exists until you correct it Hard codes indicate full time problems that are not too difficult to diagnose Ford refers to hard codes as on demand codes because they are detected by the computer immediately on demand when it runs a self test A hard code enables you to go right to a certain area or areas and begin pinpoint testing Carmakers diagnostic charts or pinpoint test procedures are designed to troubleshoot hard codes The procedures assume that the problem is present at the time of testing Soft Codes A soft code or memory code indicates an intermittent problem one that comes and goes Soft code
9. check for alternator or other brake system waming lamps The ABS lamp may go out within 1 or 2 seconds of turning on the ignition or it may stay lit for a longer time If the lamp does not light when the ignition is tumed on the computer probably will not go into the diagnostic self test mode The problem may be as simple as a burned out bulb or the problem may be with the computer itself Begin by checking the bulb Then test the lamp circuit for correct power and ground Follow the specific carmaker s instructions for checking the lamp to verify that the system can perform its self test functions If the warning lamp lights steadily with the engine running it indicates that a system prob lem exists The following section on trouble codes explains the differences between hard and soft codes and permanent and intermittent faults On many vehicles some system problems will set a trouble code in the computer memory but will not light the warning lamp 425 Sometimes the best source of information about a vehicle is ignored the owner driver Before getting all wrapped up in all the possibilities check the brake fluid level Some ABSs will switch on both warning lights if the fluid is low Special Tools Service manual Scan tool with ABS cartridge diagnostic trouble code DTC a numerical code generated by an electronic control system that has self diagnostic capabilities as the result of a system self test or moni
10. different systems however Some nonintegral ABS installations can be bled in the same way as a non ABS hydraulic system with no extra steps 419 Special Tools Service manual Special Tools Service manual Service manual Tubing with transparent container Scan tool with ABS cartridge Coworker On most ABSs a coworker can speed up the bleeding process especially if the vehicle is raised Fill level with charged accumulator x A Maximum MAXIMUM _ fill line Figure 9 4 The hydraulic reservoir used with the early Ford Teves M ark II ABS has two fill marks One indicates the normal level with a charged accumulator the other is a M AX fill level mark On the other hand on some integral systems such as the Teves Mark II ABS the rear brakes must be bled with a fully pressurized accumulator The ignition must be on and the brake pedal must be applied while the rear bleed screws are opened one at a time Because of the procedure variations that exist you should check the manufacturer s instructions before bleeding a system that you have not worked on previously The details of bleeding procedures can change from one model year to the next so reviewing the carmaker s instructions is always a good idea WARNING If a system requires that a high pressure accumulator be charged to bleed the brakes follow the manufacturer s instructions and precautions exactly when working with high pressure hydr
11. scale NOTE You must refer to the appropriate manual to perform the following procedures Measure the resistance across the two wires of the sensor connector Is this resistance value within the specification listed in the manual Set the DMM to read dc voltage Measure the voltage across the harness side of the connector Right front speed sensor voltage What is the purpose of this voltage Reconnect the speed sensor Back probe the side of the connector Did the voltage drop Record your measurement The voltage you measure is what the ABS control module senses when it conducts a test for sensor electrical continuity The voltage is lower because most of it is being dropped across the resistance of the sensor If there is an open in the circuit the module measures the full bias voltage 449 13 14 15 16 17 18 Lower the vehicle so that the tires are approximately 5 inches off the ground Using an oscilloscope back probe the and cavities of the ABS module harness for the wheel speed sensor of the driven wheel Have an assistant start the vehicle and accelerate to 10 mph and maintain that speed Observe the amplitude and frequency of the generated signal while your assistant accelerates and decelerates the wheel Have your assistant release the accelerator pedal apply the brakes and turn off the engine In the chart provided below draw the sine wave you observed at 55 mph
12. sequence and then retest the system until no more codes appear If you determine that a code is a hard code you can go to the manufacturer s test or trou bleshooting chart for that code number If you determine that a code is a soft code use the inter mittent diagnostic procedures outlined later in this chapter to help pinpoint the problem All carmakers advise that trouble codes should be diagnosed and serviced in a basic order hard codes first followed by soft codes 427 hard code a diagnostic trouble code from a vehicle computer that indicates a problem that is permanently present at the time of testing may or may not keep the system from operating soft code a diagnostic trouble code from a vehicle computer that indicates a problem not present at the time of testing indicating an inter mittent problem that occurred some time before testing stored in long term computer memory and usually erased after fifty to one hundred ignition cycles if the prob lem does not recur The terms hard code and soft code also apply to DTCs that are stored by the vehicle s PCM Special Tools Service manual Scan tool with ABS cartridge Digital multimeter Operating Range Tests Special Tools The signal from an analog sensor can drift out of range as the sensor ages or wears Some sensors Service mahual can develop an erratic signal or dropout at one point in the signal range A loose or corroded ground co
13. signal interference Figure 9 20 shows a simple speed sensor bias voltage circuit that uses a pull up resistor inside the computer The bias voltage varies from manufacturer to manufacturer It may be the 5 volts used for other computer circuits or it may be a different value such as 1 5 volts or 1 8 volts Check the carmaker s test procedures and system specifications to determine the required bias voltage when troubleshooting a speed sensor circuit Lb do Fie 4 Analog type scope Digital type scope Figure 9 19 An oscilloscope is the best tool for analyzing a speed sensor signal 436 Speed sensor magnetic pickup Pull up resistor Sensor bias voltage Signal monitor Figure 9 20 Simplified speed sensor circuit showing bias voltage and the signal monitor point The computer monitors the sensor signal at a point between the fixed pull up resistor and the pickup coil Figure 9 20 When power is applied to the circuit current flows through the pull up resistor and through the pickup coil to ground The voltage drop at the signal monitor point is a predetermined portion of the reference voltage and a known value that is part of the com puter program If an open circuit exists no current flows through the circuit and no voltage is dropped across the pull up resistor The signal monitor voltage will be high equal to open circuit bias volt age Figure 9 21 In this case the computer will immediately set
14. test and evaluate the signal voltage from an ABS speed sensor is to view the signal waveform with an oscilloscope Figure 9 19 Discon nect the sensor hamess from the vehicle wiring harness and connect the oscilloscope or graphing meter leads across the two terminals of the sensor harness Then rotate the wheel by hand or by using the vehicle power train as appropriate A good sensor signal should be continuously simi lar to the waveform shown in Figure 9 13 Observing the signal while the sensor is operating lets you look for intermittent problems such as erratic frequency changes or unstable waveforms Damage to the trigger wheel can pro duce an uneven signal that you could not see without operating the sensor A low amplitude sig nal also will be very clear when viewed on an oscilloscope or a graphing multimeter Checking Speed Sensor Bias Voltage A pickup coil speed sensor can generate a signal voltage through the electromagnetic action of the rotating trigger wheel and the magnetic field surround ing the coil winding It does not need a reference voltage provided by the computer as a resis tive sensor does However most ABS speed sensors receive a bias voltage from the system computer for two reasons d The bias voltage lets the system computer detect an open or a short circuit for the sensor before the wheel turns d The bias voltage elevates the sensor signal off the common ground plane of the vehicle electrical system to reduce
15. the Vehicle Being Worked On Year Make Model VIN Engine type and size Procedures If vehicle is FWD set transaxle to neutral and ignition to accessory position Lift the vehicle until one of the front wheel sensors is accessible Turn wheels to left or right for better access to the sensor Locate and disconnect the speed sensor Program the multimeter if necessary according to its operator s manual Connect the multimeter leads to the terminals on the sensor OuURWNE a S SERVICE TIP Ifthe multimeter operator can stay clear and keep the leads clear of 4 the wheel a coworker can rotate the wheel using the engine NOTE If the multimeter has a printer or data storage capabilities use either or both to print or save the graphs 7 Rotate the wheel at a constant speed while observing the graph General results 453 8 Speed the wheel faster while observing the graph General results 9 Stop the wheel s 10 After the wheel s have stopped disconnect the multimeter and reconnect the hamess to the sensor 11 Lower the vehicle 12 Shift the transaxle to park switch the ignition to off and set the parking brakes 13 Record the operational action of this speed sensor and make any recommendation v Instructor s Check 454 Job Sheet 28 Name Date Replace an ABS Wheel Speed Sensor Upon completion and review of this job sheet you sh
16. General ABS Service Upon completion and review of this chapter you should be able to T Inspect and test the brake system to O Use a computer pin voltage or pin out determine if a complaint is related to the chart to perform voltage and resistance base brakes system or the antilock system tests on computer control circuits T Relieve high pressure from an ABS 4 Perform resistance and voltage waveform hydraulic accumulator tests on a speed sensor and its circuit T Bleed an ABS 1 Remove and replace a wheel speed T Explain the purposes and major features Sensor of diagnostic trouble codes 1 Remove and replace an ABS computer T Explain the differences between hard and control module soft trouble codes Service Skills The basic concept of ABSs dates back to the 1950s but digital electronic control was not avail able until the 1980s ABSs were installed on slightly more than 3 percent of domestic vehicles pro duced in 1987 on more than 50 percent by 1995 and almost all new vehicles built for the year 2000 had ABSs As ABS use grows the variations in designs will continue For this reason you must have the manufacturer s specifications service instructions and electrical circuit diagrams for the system you are servicing ABSs are more likely to suffer from basic brake system problems than from problems in the ABS control circuitry or components which means you should be familiar with the normal brak ing system and how
17. Then analyze the data in the shop to try to locate the cause Switch and Speed Sensor Testing ABS control systems receive relatively simple input signals compared to power train control sys tems Input signals for an ABS computer or control module come principally from switches and speed sensors The following sections outline common troubleshooting guidelines for these com mon devices Switch Testing The brake switch the cruise control switch and the brake fluid warning switch are examples of ABS input signals that come from simple switches When used as a control system sensor a switch provides a digital on off high low voltage signal Such a signal indicates either one or the other of two operating conditions such as brakes released or brakes applied To provide this kind of input signal the switch may be installed between the battery and the computer or between the computer and ground If the switch is installed between the computer 430 Pull up resistor Signal _ te high Controller switch open high voltage signal Controller switch closed low voltage signal Figure 9 10 The basic switch circuit used to provide an on off input signal to a computer and ground a reference voltage is applied to the switch circuit inside the computer across a fixed resistor Figure 9 10 A pull up resistor creates the on off condition that can be recognized as a digital signal The fixed resistor is often ca
18. a specific year make and model Teves Mark II You can bleed the Teves Mark II system manually or with pressure equipment You can bleed the front brakes with or without system accumulator pressure but the accumula tor must be fully charged to bleed the rear brakes manually The ignition must be on and the brake pedal must be applied while the rear bleed screws are opened one at a time Because of the high pressure at the bleed screws you must be very careful when opening a screw to bleed the line Within 10 seconds after opening the screw the fluid flow should be free of air bubbles and the screw can be closed Refill the reservoir after bleeding each wheel The pump will run periodically during the bleeding procedure to maintain accumulator pressure Teves Mark IV Standard non ABS manual or pressure bleeding methods can be used for this system Unlike the Teves Mark II system the accumulator of the Mark IV system must be depres surized before bleeding the rear brakes The bleeding sequence varies for different years makes and models Proper bleeding for these systems consists of first manually bleeding the base brakes then bleeding the hydraulic control unit and finally repeating a manual base brake bleeding sequence Refer to manufacturers recommended brake bleeding procedures for these systems a S SERVICE TIP Before forcing a caliper piston back into its bore to remove the caliper d or change the pad attach a bleeder hose to th
19. aged wheel speed sensors and damaged sensor wiring d harnesses are a leading trigger to turn on ABS warning lamps Do not rush to con demn the ABS computer or hydraulic module before checking the speed sensors and their signals carefully a S SERVICE TIP A poor ground connection for the ABS controller will generally lead d to the storage of multiple nonrelated codes Troubleshooting Trouble Codes Automotive computers can test their own operation and the operation of input and output circuits Most computers have one or more of the following self test capabilities 1 They can recognize the absence of an input or output signal or a signal that is continuously high or low when it should not be 2 They can recognize a signal that is unusual or out of limits for a period of time or a signal from one sensor that is abnormal when compared to the signal from another sensor 3 They can send a test voltage signal to a sensor or actuator to check a circuit or they can operate an actuator and check the response of a sensor 426 If the computer recognizes a condition that is not right it records a diagnostic trouble code DTC A DTC is a 2 3 4 or 5 digit numeric or alphanumeric code that indicates a particular system problem Most systems will light the ABS warming lamp for many but not all codes In addition most ABS computers will store the code in long term memory A DTC can indicate a problem in a particular circuit or subsystem
20. al system as well as to detect open and short circuit problems Ford Motor Company particularly favors this type of signal biasing Figure 9 23 and Figure 9 24 are signal waveforms from a rear antilock brake system RABS speed sensor Note that the waveforms in both figures are evenly shaped sine waves High resis tance in the circuit of Figure 9 23 created a trouble code by offsetting the signal voltage too high above the zero voltage point shown by the small rectangle at the right side of the waveform and reducing the signal amplitude The programs for many Ford control systems require that a biased ac signal voltage still must cross a certain amount below the zero point of the voltage scale The signal in Figure 9 23 barely Year 00 Manufacturer Ford ov Model Explorer Engine 4000c Component RABS sensor Waveform Good 5V slope Figure 9 23 Faulty RABS speed sensor signal 438 Year 00 Manufacturer Ford ov Model Explorer Engine 4000c Component RABS sensor Waveform Bad 5V slope Figure 9 24 Good RABS speed sensor signal drops below zero volts The signal in Figure 9 24 on the other hand clearly drops below zero volts to the negative side of the scale and has a greater amplitude than the signal in Figure 9 23 The circuit conditions shown in these two illustrations can only be seen when bias voltage is applied to the circuit and the sensor is operating An oscilloscope or a graphing multime
21. aminated front brake pads pinched lines or leaking seals continues Figure 9 3 An experienced technician can tell a great deal about the condition of a brake system just by the pedal feel 417 Troubleshooting at the Brake Pedal cont SYMPTOM Excessive pedal effort PROBABLE CAUSE Insufficient engine vacuum defective booster vacuum leak frozen piston contaminated or glazed linings Rear brakes drag Misadjusted parking brake rear brakes out of adjustment weak shoe retum springs frozen wheel cylinder pistons All brakes drag Frozen brake pistons misadjusted stoplamp switch restricted pedal return defective master cylinder contaminated brake fluid Low speed disc brake squeak Wor pad lining Scraping noise when brakes are applied Brake linings completely worn out Intermittent chirp when drum brakes are applied Insufficient backing plate pad lubricant Intermittent clunk when drum brakes are applied Threaded drums Rear wheel lockup Pedal low and spongy with excessive pedal travel Contaminated linings front calipers frozen defective combination valve Insufficient fluid in system air in hydraulic system Pedal low and firm with excessive pedal travel Brakes out of adjustment Brakes release slowly and pedal does not fully return Frozen caliper or wheel cylinder pistons defective drum brake return springs binding pedal linkage Brakes d
22. at the left rear wheel locked under normal braking and the ABS activated with a lot of noise It made this loud knock knock tick tock noise said the driver The tech who did the brake job retested the truck and sure enough found premature ABS activation Any noises seemed normal for an ABS installation however The tech checked his service procedures again and found that the ABS computer had adaptive mem ory that needed to be reset The best way to do this was with a scan tool which the tech did After he reset the computer adaptive memory and drove the truck several miles to seat the rear brake shoes to the refinished drums the tech retumed the truck to its owner No fur ther complaints were heard Terms to Know Amplitude Diagnostic trouble code DTC Hard code Permanent magnet PM generator Reference voltage Pickup coil sensor Reluctance sensor Pull up resistor Soft code 444 ASE Style Review Questions 1 Technician A says that an ABS problem can cause the electronic control module to shut off or inhibit the system Technician B says that a loss of hydraulic fluid or power booster pressure will disable the ABS Who is correct A A only C Both A and B B B only D Neither A nor B Which of the following is NOT true about servicing ABS components or the entire system A Before beginning service depressurize the accumulator by pumping the brake pedal with the ignition off until the peda
23. at the test voltmeter should read If the switch is easily accessible you also can remove or disconnect it from the circuit and check continuity with an ohmmeter or self powered test lamp Figure 9 12 431 reference voltage a fixed voltage supplied to the sensor by a voltage regulator inside the computer or control module as the sensor changes the return voltage isaltered and sent back to the computer for use pull up resistor a fixed resistor in a voltage divider circuit for a sensor input signal a variable resistor sensor changes its voltage drop proportionally to the quantity being measured and the pull up resistor drops the rest of the reference voltage Different manufacturers may refer to reference voltage as VREF or REFV Back probe at connector Figure 9 11 Back probe the switch circuit at the computer harness connector and operate the switch to test the input voltage signal Figure 9 12 Use an ohmmeter or self powered test lamp to check continuity with the switch disconnected from the circuit 432 Figure 9 13 Typical ac sine wave voltage signal produced by a pickup coil speed sensor Speed Sensor Testing Speed sensors for antilock brake systems are voltage generating sensors called pickup coil sensors reluctance sensors and permanent magnet PM generators All work as did the earliest pickup coils in electronic distributors As a toothed reluctor ring rotates past
24. aulic components Some manufacturers state that either pressure bleeding or manual bleeding is acceptable for their various ABS installations Others specify either one method or the other WARNING Do not use DOT 5 silicone brake fluid in an ABS ABS operation will be degraded Use the DOT 3 or DOT 4 brake fluid specified by the vehicle manufacturer When bleeding an ABS hydraulic system it is good practice to flush the system completely to ensure that all old fluid and possible contamination are removed a S SERVICE TIP If a brake pull problem develops after bleeding an ABS completely flush and bleed the system again If sludge or dirt of any kind gets trapped in antilock brake solenoids or valves it can unbalance hydraulic pressure at the wheels even for non ABS braking Flushing the dirt out of the system often solves an antilock brake pulling problem The following paragraphs summarize the special instructions for bleeding some of the most popular systems These sections do not cover all possible ABS installations however and should not be substituted for manufacturers specific procedures They do provide general guidelines and examples of ABS bleeding methods however Before bleeding any antilock system repair any conditions that would set diagnostic trouble codes and clear all codes from computer memory Bendix 9 Jeep The Bendix 9 system can be bled with pressure equipment or manually The entire system including the ac
25. car maker s service instructions for the specific wheel bleeding sequence Kelsey Hayes EBC2 RABS and RWAL The Kelsey Hayes rear wheel antilock systems used on light trucks and SUVs can be bled manually or with pressure equipment in generally the same way as a non antilock system On most systems the combination valve must be held open for pressure bleeding The modulator must be bled separately if air has entered it Some modulators have bleeder screws others require that a brake line fitting must be loosened for bleeding Because of the wide variety of trucks and SUVs on which this system has been used refer to the vehicle manufacturer s instructions for the wheel bleeding sequence Kelsey Hayes EBC4 Either manual or pressure bleeding methods can be used for this system If no air has entered the hydraulic system standard non ABS methods can be used The usual bleeding sequence is RR LR RE LF If air has entered the modulator special bleeding procedures must be used Refer to the manufacturer s service instructions for details on a specific year make and model Kelsey Hayes EBC410 Standard non ABS manual or pressure bleeding methods can be used for this system if no air has entered the hydraulic lines The usual bleeding sequence is RR LR 423 RE LE If air has entered the ABS valve assembly special bleeding procedures that require a scan tool must be used Refer to the manufacturer s service instructions for details on
26. common component replacement methods a S SERVICE TIP When doing any kind of service work on an ABS let the system be your guide M any ABS components have decals usually yellow with important service directions For example many ABS accumulators have decals with instructions on how to depressurize the system before opening the hydraulic lines or checking fluid level The decals are there for your benefit Pay attention to them 439 Service manual Wiring diagram Electronic component locator Lift or jack with stands Photo Sequence 15 Pump and Motor Removal E P15 1 You will need fender covers a combination wrench set a flare nut wrench set a syringe and fresh brake fluid P15 4 Disconnect the electrical connec tors from the pressure switch and the motor if P15 7 Disconnect the high pressure hose from the pump P15 2 Place the fender covers on the vehicle and disconnect the battery ground negative cable P15 5 Use a clean syringe to remove about half of the brake fluid from the reservoir P15 3 Press and release the brake pedal thirty to forty times to depressurize the accumulator The pedal should become firmer and travel less when the accumu lator is depressurized P15 6 Unscrew the accumulator from the hydraulic module Then remove the O ring from the accumulator P15 8 Disconnect the wire retaining clip Then pull the return hose out of the pump body P15 9
27. cumulator pump and master cylinder must be bled if any hydraulic connection is opened To bleed these hydraulic control components loosen the fittings on the side of the hydraulic modulator one at a time while an assistant holds steady pressure on the brake pedal Bleed the accumulator pump and master cylinder before bleeding the wheel brakes 420 To bleed the wheel brakes turn the ignition off and pump the brake pedal thirty to forty times to exhaust accumulator pressure Leave the ignition off and the accumulator depressurized while bleeding the brakes The usual bleeding sequence for the Bendix 9 system is modulator RR LR RE LE Bendix 10 The Bendix 10 system can be bled with pressure equipment or manually Before bleeding the wheel brakes tum the ignition off and pump the brake pedal thirty to forty times to exhaust accumulator pressure Leave the ignition off and the accumulator depressurized while bleeding the brakes The usual bleeding sequence for the Bendix 9 system is LR RR LE RF Bendix 6 If the hydraulic modulator is not removed or otherwise exposed to air the bleeding procedure for the Bendix 6 system is the same as for the Bendix 10 system If air has entered the modulator special procedures beyond the scope of this manual are needed to purge the air from the system Refer to a Bendix DaimlerChrysler shop manual or aftermarket service manual for the specific year and model of vehicle being serviced Bendix LC4 Th
28. e Bendix LC4 system can be bled only manually Pressure bleeding equipment does not produce pressure high enough to remove all air from the system The usual bleeding sequence is RR LE LR RE Bleeding the LC4 system is a two stage process that requires the use of a scan tool Several aftermarket scan tools provide the necessary capabilities Follow the instructions for your partic ular service equipment Bendix ABX 4 Unless air has entered the modulator you can bleed the Bendix ABX 4 system as you would a non antilock system You can use either manual or pressure bleeding methods but Bendix 4 and ABX 4 systems are best bled manually The usual bleeding sequence is LR RE RR LF If air has entered the hydraulic modulator bleed the wheel brakes first and then bleed the modulator using a scan tool to control system operation Follow the instructions for your partic ular service equipment After bleeding the modulator repeat the bleeding operations at all four wheels To thoroughly purge these systems however you also must cycle certain solenoid valves while holding down the brake pedal Do this only when a Bendix 4 and ABX 4 brake bleeding procedure in a DaimlerChrysler service manual instructs you to do so Bendix Mecatronic You can bleed the Bendix Mecatronic system using either manual or pressure bleeding methods as you would a non antilock system The usual bleeding sequence is RR LF LR RE Bosch 3 Before bleeding the wheel brakes
29. e caliper bleeder screw put the other end in a container of clean brake fluid and open the bleeder That is only half the preparation however Next you have to keep old fluid from flowing back up the brake lines when you push the piston back in its bore You can do this in one of two ways You can clamp the brake hose with smooth jawed locking pliers or a similar clamp to keep sediment from flowing back up the hose or you can use the brake pedal depressor from the wheel alignment equipment to apply the brake pedal about 1 2 inch This will block the ports in the master cylinder and hold moderate pressure in the lines Then push the piston back in its bore Any sediment in the caliper bore will be forced out through the bleeder not back into the brake system where it can damage expensive ABS components General ABS Troubleshooting The following sections outline the troubleshooting principles for ABS control systems and for in dividual components These guidelines apply to all antilock systems Chapter 10 of this Shop Manual contains specific diagnostic information for specific systems You will get the most bene fit from any diagnostic guidelines if you use them as part of organized systematic troubleshoot ing The four major steps for accurate troubleshooting are 1 Basic inspection and vehicle checkout 2 Control system diagnosis trouble codes self tests and data readings 3 Operating symptom diagnosis 4 Intermittent problem dia
30. e translucent master cylinder reservoir 8 Inspect all brake hoses lines and fittings for damage deterioration leakage or chassis interference This inspection requires that the vehicle be raised on a hoist Fix any defects found 9 Finally test drive the vehicle to evaluate brake system performance Accelerate to about 20 mph and use normal braking to stop the car If you can stop it smoothly within 25 feet without swerving the brakes are probably in good working order Under hard braking beginning from 25 mph or 30 mph you may feel the brake pedal pulsate and the ABS light may come on fora moment if you incur an ABS event Troubleshooting with the Brake Pedal The brake pedal is a helpful diagnostic tool that is easily used by a trained technician You can determine the probable cause of a wide variety of brake system problems by identifying appar ent symptoms as you apply the pedal Figure 9 3 lists symptoms and probable causes that can be determined in this way Troubleshooting at the Brake Pedal SYMPTOM PROBABLE CAUSE Pedal surging brake chatter vehicle surge Front discs out of round excessive disc thickness during braking variation bearings out of adjustment Rear drums out of round hard spots caused by overheating Brakes grab Hard spots on front discs or rear drums cracked pads or shoe linings Car pulls to one side Misaligned front end drum brake components malfunctioning frozen caliper pistons or cont
31. em Technician B disconnects the battery ground cable Who is correct A A only B B only C Both A and B D Neither A nor B When first testing a car with ABS it is important to A disconnect the battery ground negative cable B apply the parking brake C note the status of the ABS warning lamp D try to lock the brakes When inspecting wheel speed sensors check for all of the following except A correct bias voltage B proper contact between the pole piece and tone ring C secure sensor mounting D condition of the tone ring teeth Technician A says that in some antilock systems the power brake assist is provided by pressurized brake fluid supplied by the hydraulic accumulator Technician B says that the accumulator holds highly pressurized nitrogen gas that is used for power brake boost Who is correct A A only B B only C Both A and B D Neither A nor B Technician A says that wheel speed sensors generate a square wave frequency signal Technician B says that a wheel speed sensor has a permanent magnet Who is correct A A only C Both A and B B B only D Neither A nor B 445 ASE Challenge Questions Use these ABS codes as directed in the following questions The codes are not for any single vehicle CODE DESCRIPTION 12 POWER INTERRUPT DURING LAST 40 STARTS 13 LEFT FRONT SPEED SENSOR VOLT LOW 14 LEFT FRONT SPEED SENSOR VOLT HIGH 15 REAR SPEED SENSOR CIRCUIT OPEN
32. ercontrolled output device should not exceed 0 75 ampere 750 milliamperes Before replacing a computer check all output circuits for shorts or low resistance that could damage the computer WARNING Be sure that the ignition is off when removing and installing a control module or other electronic component As a general rule the system computer should be at the bottom of the list of things to replace Again computers can fail but a sensor or actuator problem bad wiring or a mechanical fault in the engine is a more likely cause of a problem a S SERVICE TIP Beware of ESD when handling electronic components ESD is static d electricity that can destroy the microscopic circuits of electronic integrated circuits If you take some simple precautions however you can avoid ESD problems ESD occurs when two dissimilar materials are rubbed together or quickly separated from each other Electrical charges build up on the surfaces and then discharge when a circuit path is available If you slide across the front seat of a car and then touch a metal surface you can build up and then discharge several thousands of volts of static electricity ESD of 8 000 volts to 10 000 volts is very common and you will not even feel or see it When ESD generates a small spark from your fingertip to a metal surface and you can feel the snap you are dealing with 40 000 volts to 50 000 volts of ESD High voltage ESD does not hurt you because it is moving only a few m
33. es with a sensor circuit reduces the signal voltage of the sensor This ground resistance can offset the signal voltage enough to cause serious problems For example a 0 5 volt drop across the ground connection on a sensor that operates on a 5 volt reference equals a 10 percent measure ment error Back probe at connector Redundant grounds Figure 9 9 With any circuit closed and current flowing voltage drop across any ground connection and the battery negative terminal must be no more than 0 100 volts 100 millivolts 429 Service manual Wiring diagram Electronic component locator Service manual Wiring diagram Electronic component locator Troubleshooting Intermittent Problems Intermittent problems can be the hardest to diagnose and fix If you are lucky the intermittent problem will set a soft code in the computer memory This gives you a clue at least about the general area in which to start testing Remember however that if you clear the codes the prob lem may not recur right away You may have to simulate the conditions that caused the problem or road test the vehicle to catch the intermittent fault The following paragraphs outline some basic points that can help you troubleshoot intermittent problems Use Wiggle Tests and Actuator or Sensor Special Tests Most control systems have long term memory that will record soft codes for intermittent problems Ford recommends wiggle tests in which you put
34. es at least 9 6 volts to 10 volts during cranking Be sure the charging system 442 is maintaining correct battery charge Most computers receive battery voltage through a fuse or fusible link Be sure that battery voltage is available at the specified terminals of the computer s main connector Most computers are grounded remotely through several wires in the harness Trace and check the ground connections to ensure good continuity 2 Operation of a system power relay Some computers receive power through a system power relay If the vehicle is so equipped check the relay operation This relay may be remote mounted or undemeath the electrohydraulic plastic cover 3 Sensor reference voltage and ground circuits Many sensors share a common reference voltage supply from the computer and a common ground Incorrect or erratic reference voltage or a bad common ground can affect operation of several sensors simultaneously The symptoms may appear as if the computer has a major system problem Repairing a wiring connection may correct the problem 4 Resistance and current flow through all computer controlled solenoids and relays Every output device solenoid or relay controlled by a computer has a minimum resistance specification The actuator resistance limits the current through the computer output control circuit If the actuator is shorted current can exceed the safe maximum and damage the computer In most cases current through a comput
35. gnosis The details of these steps are nothing new or revolutionary These steps are simply up to date applications of proven test principles The following sections explain how to use these prin ciples effectively 424 Basic Inspection and Vehicle Checkout The system computer does not monitor or control all parts of the ABS You must inspect mechan ical components vacuum and hydraulic lines wiring and mechanical parts You also should check for body damage mechanical damage or tampering and newly installed accessories The following steps will make your inspection and checkout easier Verify the Customer s Complaint Get the customer to describe the problem in as much detail as possible Ask these kinds of questions 1 Does the problem exist all the time or some of the time Does it occur regularly or at random L Does the problem occur at certain times or temperatures 1 What are all the symptoms noises vibrations smells vehicle performance or any combination 4 Has the problem occurred before and what was done to fix it 1 When was the vehicle last serviced and what was done to it Listen to the customer s complaint carefully and get as much information as possible Avoid asking closed end questions such as Does it happen when the engine is hot Ask open ended questions such as What temperature is the car when this happens Finally check the vehicle yourself to verify that the problem exists as de
36. he engine and run it for 10 seconds Ver ify that the ABS lamp is off and listen for several sharp clicks that indicate the pistons being driven to their upper positions If you do not hear these distinct clicks drive the car at 5 mph and again listen for the clicking of the ABS control motors When you hear the clicks carefully drive the car to the service bay without activating ABS operation Before bleeding the wheel brakes attach a hose to the rear bleeder screw on the hydraulic modulator closest to the master cylinder and manually bleed all air from the bleeder port Fig ure 9 5 Then repeat this procedure at the forward bleeder screw After bleeding the modulator loosen all of the brake line fittings on the outboard side of the modulator and manually bleed air from the upper ends of the brake lines Figure 9 6 Bleed first ODN Op Figure 9 5 Bleed these two points on the ABS VI modulator first Courtesy of General M otors Corporation Service Operations 422 Brake line fittings Figure 9 6 Bleed air from the brake line fittings at the outboard side of the ABS VI modulator Courtesy of General Motors Corporation Service Operations The last stage of bleeding an ABS VI system is to bleed the wheel brakes either manually or with pressure equipment Because of the variations in ABS VI installations and because the system has been split either diagonally or front to rear on different vehicles consult the
37. ht and feel should remain constant as you apply and release the pedal If they change with repeated pedal appli cations air may be trapped in the brake lines If the car has vacuum assisted power brakes start the engine and run it at medium speed fora short time then shut it off Wait about 90 seconds and then apply the brake pedal moderately several times The brake pedal should feel firmer When the vacuum reserve is exhausted depress the brake pedal firmly and restart the engine The pedal should drop slightly and then hold as vacuum is applied to the booster Shut the engine off and check the master cylinder fluid level On most late model cars this can be done by cleaning the translucent reservoir and visually noting the fluid level in relation to the embossed line or mark on the reservoir Figure 9 2 To evaluate fluid condition remove the reservoir cap or cover Check the condition of the vacuum hose between the power booster and intake manifold Start the engine and listen for a hissing noise from the hose or hose connection Such a noise indicates a vacuum leak Replace the hose if it is deteriorated replace the hose clamps if the hose connections are not tight lt gt C BRAKE INFORMATION CENTER Figure 9 1 Both the BRAKE and the ABS indicator lamps should light when you turn on the ignition 416 Fluid reservoir Figure 9 2 On many vehicles you can check the brake fluid level through th
38. icroamperes of current That small amount of current however can destroy the microscopic interconnec tions of an integrated circuit Those few microamps blow the circuit as does a low current fuse You can avoid ESD problems by observing a few simple precautions when handling electronic components 4 Do not remove an electronic part from its packing material until you are ready to install it O Do not hold an electronic part by its connector pins 1 Before entering a vehicle to remove or replace an electronic part touch an exposed metal part of the vehicle to discharge any static charge from your body 443 The best method to prevent damage to electronic components from static is to always wear an antistatic strap during the repairs The strap can be worn on the wrist or may bea waist belt Some companies require their technicians to wear one as part of the uniform 4 Avoid sliding across upholstery or carpeting when removing or installing an electronic part If this is not possible touch an exposed metal part of the vehicle with your free hand before installing a new component 1 When available use an antistatic grounding strap attached to your wrist and clipped to a metal part of the vehicle body to prevent static charges from accumulating CASE STUDY The GMC Sonoma got a normal maintenance brake job including thoroughly flushing and bleeding the hydraulic system After the brake job the owner reported th
39. ing All pickup coil sensors have resistance specifications One basic test for any speed sensor is to disconnect it from its circuit and measure its resistance by connecting an ohmmeter across the two terminals of the sensor wiring harness Figure 9 18 If resistance is out of limits either high or low replace the sensor 434 Typical ac voltage waveform from a pickup coil sensor Low frequency signal Figure 9 17 Typical speed sensor voltage waveform top compared to a low amplitude signal center and a low frequency signal bottom Wheel speed sensor Figure 9 18 Use an ohmmeter to measure the resistance of the pickup coil winding 435 Special Tools Oscilloscope or scan tool with PC graphing or graphing multimeter Service manual Wiring diagram Electronic component locator A waveform is a graphic representation of a voltage signal as displayed on an oscilloscope Almost all scan tools and some graphing meters can display one or two wave forms or traces or they have the hardware to be connected to a personal computer PC A resistance test for a speed sensor is only a starting point however Sensor resistance often can be within limits but the sensor can produce a faulty signal Damage to the sensor trigger wheel tone ring for example can produce an uneven signal even when the pickup coil is elec trically in good condition Sensor Voltage Waveform Testing The best way to
40. ive and allow to idle NOTE The next step is to test the holding ability of the parking brakes If a slope is not available follow the procedures in step 10 451 9 Use a clear open sloping area Apply the parking brakes and engage neutral with the transmission Results 10 If slope is not reasonably available A Stop the car apply the service brakes and set the parking brakes NOTE If vehicle moves during the next step apply the service brakes immediately B With engine idling and transmission in drive or reverse release the service brakes Results 11 Retum the vehicle to the bay or parking area 12 Is system satisfactory at this point Explain your findings and recommendations v Instructor s Check 452 Job Sheet 27 Name Date Testing an ABS Wheel Speed Sensor Upon completion and review of this job sheet you should be able to inspect and test an ABS wheel speed sensor with a graphing multimeter ASE Correlation This job sheet is related to the ASE Brakes Test Content Area Anti Lock Brake System ABS Diagnosis and Repair Task Diagnose service and adjust ABS speed sensors and circuits following manufacturers recommended procedures includes voltage output resistance shorts to voltage ground and frequency data Tools and Materials Service manual Wiring diagram Component locator Graphing multimeter or oscilloscope Lift or jacks with stands Describe
41. l becomes hard B All base brake parts can be serviced in the same way as they would be if they were part of a non ABS C Air gaps between the speed sensors and toothed ring must be adjusted after machining the brake rotors D Wheel bearings must be adjusted properly Technician A says that it is normal for the amber ABS lamp to light when the ABS is activated during braking Technician B says that it is normal for the red BRAKE lamp to light when the ignition is first tumed on and the engine is off Who is correct A A only C Both A and B B B only D Neither A nor B When working on a vehicle with antilock brakes Technician A relieves system pressure by slightly opening a bleeder screw and allowing fluid to spray into a wide mouth container Technician B turns off the ignition and pumps the brake pedal thirty to forty times until she feels an increase in pedal pressure Who is correct A A only C Both A and B B B only D Neither A nor B Bleeding an ABS is being discussed Technician A says that cracking open the brake line connections at the hydraulic module and bleeding the air into a shop rag is the recommended procedure for some systems 10 Technician B says that pressure bleeding is required for bleeding ABSs Who is correct A A only C Both A and B B B only D Neither A nor B When removing a vehicle s ABS electronic control module Technician A relieves hydraulic pressure in the syst
42. l speed sensors can be repaired by soldering and reinsulating with heat shrink tubing Wheel sensor Polyethylene strip Figure 9 25 Some wheel speed sensors use a plastic spacer to set the air gap correctly 441 Paper air gap adjusting disc sensor Figure 9 26 Other wheel speed sensors use a paper spacer In either case the spacer should not be removed during sensor installation Because of the importance of signal accuracy from a wheel speed sensor it is generally preferable to replace a sensor assembly including the harness instead of trying to repair the har ness Consult the manufacturer s specifications before deciding how to service these components Sensor tone rings that are pressed on the inside of the rotor or on the axle shaft often can be replaced If the sensor ring is an integral part of the wheel bearing assembly hub assembly or the outer constant velocity joint on the axle the entire component must be replaced if the sensor ring is damaged Observe these additional guidelines when servicing ABS wheel speed sensors 4 Unplug sensor electrical leads when replacing suspension components 4 If a sensor tone ring trigger wheel is replaceable fit the new one in place by hand Do not hammer or tap the sensor in place d If a wheel sensor ring or tone wheel is replaceable and is pressed into place do not remove the old ring or install a new one by hammering or prying Use a hydraulic press with the p
43. lled a pull up resistor because it pulls the refer ence voltage up to the open circuit level when the switch is open and drops the voltage when the switch is closed The computer takes its input signal internally at a point between the resistor and the switch Figure 9 10 The reference voltage for the switch circuit is most often the 5 volt reference used for other computer circuits For some circuits it may be full system voltage approximately 12 volts or some other voltage level The important thing to remember is that the voltage signal to the com puter is either high or low depending on the switch position and indicates one of two operat ing states Testing a switch circuit is the basic process of placing the switch in a known operating posi tion open or closed and using a voltmeter to check the voltage signal received by the computer One common way to do this is to back probe the switch circuit wire terminal at the computer har ness connector with the positive lead of your voltmeter Figure 9 11 shows this test method with the switch both open and closed With the switch open no current flows in the circuit so no voltage can be dropped across the fixed resistor The input signal is open circuit reference voltage and that is what the test volt meter should read With the switch closed current flows through the circuit and the fixed resis tor drops all of the reference voltage The input signal is near zero volts and that is wh
44. llowing manufacturers procedures and specifications observe proper placement of components and routing of wiring harness Symptoms Possible Causes Safety Classroom Shop Manual Manual Light stays on 1 Sensors damaged Wear safety glasses 223 237 415 no ABS misadjusted Lift and jack safety 418 424 2 Service brakes incorrect procedures 439 444 3 Low fluid Follow ABS and SIRs 4 Bad switch es or circuit s safety procedures 448 Job Sheet 25 Name Date Measure ABS Component Values Upon completion of this job sheet you will have measured various ABS component electrical values Tools and Materials Scan tool Digital Multimeter DMM Oscilloscope Describe the Vehicle Being Worked On Year Make Model VIN Engine type and size Procedures AUNE UI 10 11 12 CAUTION Follow the scan tool s instructions for entering the vehicle s ID Some scan tools may clear all DTCs if it is connected to the vehicle prior to entering the vehicle ID Connect the scan tool to the vehicle data link Tum the ignition on Verify that there are no codes present If there are notify your instructor Referring to the service manual identify the location of the RF wheel speed sensor connector Where is it located Locate and disconnect the speed sensor two way connector harness for the RF wheel Connect your DMM to the sensor side of the connector and set it to the kilohm
45. nes where pressure may be present Failure to comply may result in vehicle damage or injury Depressurizing the System Relieving Accumulator Pressure You must refer to the carmaker s service procedures if you find it necessary to check brake fluid level bleed the brakes or open a hydraulic line to replace a component These service procedures will tell you if it is necessary to depressurize the hydraulic accumulator first For example the DaimlerChrysler ABS 3 system and the Teves ABS both use a pressurized hydraulic accumulator The DaimlerChrysler ABS 3 system must be depressurized to bleed the brakes but the Teves ABS requires that the accumulator be fully pressurized when bleeding the rear brakes The Teves front brakes can be bled with or without accumulator pressure When the automaker s procedure requires that the system be depressurized the ignition switch should be off Pump the brake pedal at least twenty five times with about 50 pounds of pedal force As the accumulator pressure discharges you will notice a change in pedal feel When you feel an increase in pedal effort pump the pedal a few more times This will remove all hydraulic pressure from the system Some systems may require up to fifty pedal applications to relieve accumulator pressure completely It is always better to proceed on the side of caution so apply the pedal a few more times after the pressure seems to have been relieved Fluid Level Check and Refill Some in
46. ng self diagnosis and or recommended test equipment determine needed repairs Diagnose service and adjust ABS speed sensors and circuits following manufacturers recommended procedures includes voltage output resistance shorts to voltage ground and frequency data Repair wiring harness and connectors following manufacturers procedures Problem Area Symptoms ABS LIGHT Light stays on no ABS Possible Causes 1 Sensors damaged misadjusted Service brakes incorrect Low fluid ole Ww N Corroded damaged connections Bad switch es or circuit s Safety Classroom Manual Wear safety glasses 228 232 Lift and jack safety procedures Follow ABS and SIRs safety procedures 447 Shop Manual 415 418 424 430 Shop Manual 415 424 443 Table 9 3 ASE TASK Problem Area ABS LIGHT Follow accepted service and safety precautions when inspecting testing and servicing of ABS hydraulic electrical and mechanical components Depressurize integral high pressure components of the ABS following manufacturers recommended safety procedures Fill the ABS master cylinder with recommended fluid to proper level following manufacturers procedures inspect system for leaks Bleed the ABS hydraulic circuits following manufacturers procedures Perform a fluid pressure hydraulic boost diagnosis on integral high pressure ABS determine needed repairs Remove and install ABS components fo
47. nnection for a sensor also can force the signal out of limits These sensor problems and similar problems can cause definite malfunctions without setting a code You can check the operation of many sensors however by using the operating range Digital multimeter charts provided by the carmakers These charts list signal range specifications for voltage resis tance frequency or temperature that the sensor provides under varying conditions Use a DVOM a frequency counter or other appropriate instrument to test the sensor sig nal at the sensor connector and if necessary at the main connector to the computer You can back probe many sensor connectors or install jumper wires to provide connection points for your meter You may need a breakout box or harness to check sensor signals at the main com puter connector If possible operate the sensor through its full range and check the signal at several points Scan tool with ABS cartridge Wire harness connector end views E Antilock brake control module connector harness inside Pin l 530 Ground LG Y Pin Number Circuit s nouses o 535 LB R ABS Switch to Level Switch No 2 2 498 PK _ ABS Valve Assembly 27 524 Right Rear Brake Antilock 532 O Y ABS Power Relay PK BK Sensor LO 549 Antilock Brake Pedal Sensor LG BK Sensor LO BR W Switch are Right Front Brake Antilock ea Not Used 30 522 T BK Left
48. ould be able to replace an ABS wheel speed sensor ASE Correlation This job sheet is related to the ASE Brakes Test Content Area Anti Lock Brake System ABS Diagnosis and Repair Task Diagnose service and adjust ABS speed sensors and circuits following manufacturers recommended procedures includes voltage output resistance shorts to voltage ground and frequency data Tools and Materials Service manual Lift or jack with stands Impact tools Describe the Vehicle Being Worked On Year Make Model VIN Engine type and size Procedures 1 Determine Wheel sensor fastener torque Wheel lug nut torque Special tools and procedures for setting air gap Lift vehicle to a good working height Remove the wheel assembly Inspect the area around the speed sensor Remove any component blocking access to the speed sensor and or fasteners Items removed if any U A WN 6 Remove the speed sensor 7 Inspect the tone ring as much as possible Results Remove the new speed sensor from its shipping carton 9 Install the speed sensor into its mounting 455 10 11 12 13 14 15 Secure the special tools and set the air gap to specifications Install and torque the speed sensor fastener Install the wheel assembly and torque the lug nuts to specifications Lower the vehicle Clear any ABS codes and road test When the repair is complete clean the area
49. ppropriate service manual DMM Special Tools Coworker The ABS warning light is amber To check the base brake system 1 Start the engine and note the brake and ABS indicator lamps When you turn the ignition switch on the BRAKE lamp should light with the parking brake off The ABS indicator lamp should light for a few seconds then go out Figure 9 1 Apply and release the parking brake The BRAKE lamp should light when the parking brake is applied and go out when it is released The ABS indicator lamp should light while the engine is cranking and go out when it starts On some systems it may remain on for a few seconds after the engine starts then go out Check the operation of the stoplamps by pressing the brake pedal while an assistant watches both fender mounted lamps and the CHMSL to make sure they light when the pedal is applied and go off when the pedal is released With the engine running pump the brake pedal rapidly several times The pedal height should remain about the same If it increases during pumping or if you note a very spongy feeling during pedal application air may be trapped in the hydraulic lines It is common for the brake pedal on a car with antilock brakes to feel slightly softer than a car without them On many systems you can force the pedal to the floor with firm pressure The important thing to check for is the uniformity or repeatability of the brake pedal operation Pedal heig
50. rag and pedal does not fully return Contaminated brake fluid defective master cylinder defective vacuum booster or vacuum check valve binding pedal linkage or lack of lubrication Figure 9 3 Continued CUSTOMER CARE Advise your customers that pumping the brake pedal on a vehicle with antilock brakes actually defeats the operation of the antilock system ABS Hydraulic System Service When you service the non antilock part of some ABS installations you must take certain precau tions You must understand the system components and their operation before you try to bleed the brakes or perform other service that requires opening the hydraulic system An integrated ABS installation using a pressurized accumulator is similar to the hydro boost power brake system that uses the power steering fluid to operate both the steering gear and the 418 brake booster In both designs the hydraulic fluid is under very high pressure For example 2 600 psi of hydraulic pressure exists in the DaimlerChrysler ABS 3 system whenever the ignition switch is on Opening a hydraulic line in this system without first discharging the pressure can result in a messy and potentially dangerous situation WARNING Before opening the hydraulic system of an ABS installation review the manufacturer s service instructions with particular attention to safety precautions that relate to hydraulic pressure Do not loosen any fittings or otherwise open hydraulic li
51. roper special tools Ly Remove the vehicle wheel when replacing a wheel sensor 1 Some wheel sensors require an anticorrosion coating before installation to prevent galvanic corrosion Never substitute grease unless the carmaker specifies its use Sensor assemblies that are a permanent part of the wheel bearing and hub assembly are used on many late model GM cars They need no adjustment and plug directly into the vehicle wiring hamess Computer Control Module Replacement Vehicle computers do fail but not with great frequency or regularity Too many computers have been replaced because someone thought it might be the problem or didn t know what else to do Too often computer replacement does not cure the problem The shop has spent several hundred dollars and still has a car to fix Before deciding to replace a computer you should check the manufacturer s technical service bulletins TSBs for specific information on revised computer part numbers and the problems they were designed to correct Also check with dealership parts departments for the latest part number information Computers and other electronic parts usually are special order items All electronic parts are absolutely positively nonreturnable Once pur chased they are yours To avoid costly unnecessary computer replacement check these items 1 Battery voltage supply to the computer and the main system ground Be sure the battery is fully charged and provid
52. s are the computer s way of remembering a problem that occurred sometime in the past before testing but that is not present now The problem may not reappear if you clear the codes and retest the system It may have happened at a certain speed or temperature or under some other conditions that you cannot recreate in the shop Ford refers to soft codes as continuous memory codes because they are stored continuously in the computer s memory until cleared Some GM divisions call soft codes on late model vehicles history codes and identify them as such on the computer s data stream Because soft codes indicate intermittent problems diagnostic charts and pinpoint tests usu ally do not isolate the problem immediately The special intermittent test procedures later in this section will help you troubleshoot soft codes accurately To find the problems that cause soft codes you should not open or disconnect electrical connectors until you have checked them in normal operation or by doing a wiggle test Disconnecting and reconnecting a connector may tem porarily solve a problem without revealing the basic cause Determine Whether Codes Are Hard or Soft After checking trouble codes write down any codes that may be present Remember that if you clear the codes soft codes will not reappear right away Some antilock systems will display only one or up to three codes at a time even when more faults exist For such systems you must repair and clear each code in
53. scribed Try to recreate the conditions that the customer describes You may not always be able to duplicate the conditions exactly but try to come as close as possible You may have to road test the vehicle or you may have to leave it standing overnight to recreate a cold operating problem If the problem caused a soft code try to get the code to recur during testing Inspect and Check Out the Vehicle Look for obvious faults and try to eliminate simple prob lems first Look for loose or broken wires connectors and hydraulic lines or hoses Check for leaks Check for mechanical and electrical tampering and collision damage After you have completed the basic inspection and checkout of a system you can move into control system diagnosis Test the Control System Test from the general to the specific If you immediately look at the computer system for the cause of a problem you can overlook other possible causes The basic inspections and tests described in other sections of this Shop Manual begin with general checks or area tests Testing the computer control system also should begin with general area tests before moving on to pinpoint tests Check the System Warning Lamp Vehicles with ABSs have an amber or yellow instrument panel lamp that lights to indicate major system problems Figure 9 7 Any such indicator lamp should light when the ignition key is turned on without starting the engine This is a basic bulb check similar to the bulb
54. tance sensor a magnetic pulse generator or pickup coil that sends a voltage signal in response to varying reluctance of a magnetic field permanent magnet PM generator a generator that generates a voltage signal by moving a conductor through a permanent magnetic field amplitude signal strength or the maximum measured value of a signal Integral wheel speed sensor Figure 9 15 Rear wheel speed sensor installation Integral type ABS Ov ac voltage waveform converted to a square wave signal Figure 9 16 The computer converts the sine wave to a square wave to measure signal frequency an oscilloscope scope is the height above and below the reference line usually labeled zero 0 Although the signal frequency or speed varies with the wheel speed it must be smooth and oper ate at a uniform amplitude Figure 9 17 shows an example of a typical speed sensor voltage sig nal along with examples of low amplitude and low frequency signals A variation in speed signal frequency or a speed difference between the wheels is the nor mal trigger for antilock operation An uneven or erratic frequency signal also can trigger a sys tem trouble code A normal speed sensor signal should be a repeatable ac voltage as shown in Figure 9 13 with the frequency varying smoothly with wheel speed A missing signal a low amplitude signal or an erratic frequency signal can cause a system trouble code Sensor Resistance Test
55. tegrated antilock systems require different procedures to check and refill the fluid reser voir The DaimlerChrysler Bosch ABS 3 system must be depressurized before the reservoir cap is removed The fluid level should be at the top of the white screen in the filter and strainer assembly To check fluid level in an early Teves Mark II system turn the ignition on and pump the brake pedal until the hydraulic pump motor starts When the pump shuts off you can visually check the level through the translucent reservoir Under certain conditions the fluid level may be above the MAX fill line on the reservoir If this is the case shut the ignition off and then tum it back on Pump the brake pedal again to start the hydraulic pump When the pump stops the fluid level should be accurate If the fluid is below the MAX fill line Figure 9 4 remove the cap and add enough fluid to bring it to the correct level To check the fluid level on later Teves systems depressurize the system and look at the fluid through the translucent reservoir The level should be at the FULL mark With the system pressurized the level will be somewhere below the FULL mark Do not overfill the reservoir in either system This will cause the fluid to overflow when the accumulator discharges during its normal operation Bleeding the System Bleeding an ABS is fundamentally the same as bleeding a non ABS hydraulic system Some vari ety exists in extra steps that may be required for
56. ter is an important tool for troubleshooting these kinds of problems in any ABS speed sensor circuit ABS Component Replacement Troubleshooting and diagnosis are larger factors in ABS service than is component replacement Preceding sections of this chapter provide general guidelines for the most common trouble shooting requirements Vehicle manufacturers also provide specific test procedures for specific components in their service manuals Look for this information in carmakers service manuals or aftermarket information sources When a component does require replacement the methods are generally straightforward mechanical procedures Some special tools may be needed to service some ABS components You can find this information along with replacement procedures in manufacturers and after mar ketservice manuals WARNING ABS service may require opening the hydraulic system ABS hydraulic systems may operate with pressures of 2 000 psi or higher The system must be com pletely depressurized before opening any hydraulic connection In most cases you can depressurize the system by applying and releasing the brake pedal at least twenty five times Follow the vehicle manufacturer s instructions for complete information on hydraulic system service and safety Photo Sequence 15 shows the key steps of a typical ABS pump and motor removal This sequence outlines basic pump service for a GM Teves system These or similar steps are examples of
57. th A and B D Neither A nor B Three channel four wheel ABSs are being discussed Technician A says code 18 above chart and a lit waming light indicate the brake lights are not working Technician B says code 16 above chart and a lit warming light indicate that the rear ABS is disengaged but the front circuit should still be working Who is correct A A only B B only C Both A and B D Neither A nor B 446 Table 9 1 ASE TASK Follow accepted service and safety precautions when inspecting testing and servicing of ABS hydraulic electrical and mechanical components Diagnose poor stopping wheel lockup pedal free and travel pedal pulsation and noise problems caused by the ABS determine needed repairs Problem Area Symptoms WHEELS LOCK Wheels lock under POOR BRAKING normal braking pedal feels uneven Possible Causes 1 Damaged misadjusted wheel speed sensor 2 Low brake fluid 3 Modulator inoperative 4 Service brake incorrect Table 9 2 ASE TASK Safety Classroom Manual Wear safety glasses 65 66 Lift and jack safety 229 233 procedures Follow ABS and SIRs safety procedures Follow accepted service and safety precautions when inspecting testing and servicing of ABS hydraulic electrical and mechanical components Observe ABS warning light s at startup and during road test determine if further diagnosis is needed Diagnose ABS electronic control s components and circuits usi
58. the car computer and a scan tool in communication so that the scan tool will indi cate when a soft code is set You can then tap or wiggle wiring and connectors to try to get the problem to occur If you do get the problem to occur remember what you did when the code set Use the scan tool to read the codes from the car again to verify the fault Many vehicles have special tests that let you command the computer to switch actuators on and off for testing Some scan tools for example allow you to operate the pumps of the Delco Moraine ABS VI system for bleeding Check Connectors for Damage Many intermittent problems are caused by damaged connec tors and terminals Unplug the connectors in the problem circuit and inspect them carefully for 4 Bent or broken terminals 4 Corrosion 4 Terminals that have been forced back in the connector shell causing an intermittent connection O Loose frayed or broken wires in the connector shell NOTE Do not use spray electrical contact cleaner on a harness connector unless the wiring harness has been disconnected from the ABS controller Electrostatic discharge EDS may dam age the ABS controller Road Test and Record Data If the vehicle transmits computer data in a road test or normal operating condition and most ABS computers do drive the vehicle and try to duplicate the problem Use the snapshot or data recording function of a scan tool to record the computer data when the problem occurs
59. the sta tionary sensor it produces a voltage frequency and intensity directly proportional to wheel speed As the teeth of a rotating trigger wheel pass by the magnet the magnetic field expands and collapses to generate an ac voltage in the coil Figure 9 13 This signal is sent to the elec tronic module which processes it to determine rotational speed Whether the speed sensor is mounted on a wheel or inside the transmission or differential it works on these same principles Figure 9 14 and Figure 9 15 are photos of cutaway wheel speed sensor installations for front and rear disc brakes ABS speed sensors produce an ac sine wave voltage signal which is typical of any pickup coil sensor The computer converts the ac sine wave voltage to a digital square wave signal so that it can read the sensor frequency or speed Figure 9 16 The computer simply counts the trailing or falling edge of the square wave signal to determine wheel speed The ac sine wave signal from the speed sensor must have a certain amplitude and a smooth frequency within its specified operating range The amplitude is the strength of the signal or the positive and negative height of the voltage waveform The amplitude of a signal being shown on Wheel speed sensor Figure 9 14 Front wheel speed sensor installation 433 pickup coil sensor a reluctance sensor that generates a voltage signal by moving a conductor through a permanent magnetic field reluc
60. to diagnose its problems Some ABS installations require special testers to read trouble codes and perform some system tests If the required tester is not available you can troubleshoot many of the circuits with ordinary test equipment but your diagnosis will not be as fast or as efficient This chapter contains basic ABS troubleshooting information as well as general test and repair guidelines that apply to most systems Chapter 10 in this Shop Manual contains specific control system diagnostic information for antilock systems used by domestic carmakers Brake System Troubleshooting An ABS is an electrically controlled hydraulic system The ABS function will not work if the brakes do not work properly in their non antilock mode Some ABS problems will be electrical but many will result from a hydraulic system malfunction When such problems are detected by the ABS control module it will disable the antilock function and light the antilock indicator lamp on the instrument panel The cause can be as simple as a low hydraulic fluid level or a leaking hose line or connection Brake System Check Use the following quick and simple brake system check to help you determine if the base brake system is working properly and whether the problem is electrical or hydraulic You have already learned several of these tests earlier in this manual as checks for the base brake system 415 CHAPTER Basic Tools Basic technician s tool set A
61. toring to indicate a problem in a cdircuit or subsystem or to indicate a general condition that is out of limits also called trouble codes service codes or fault codes by various carmakers Figure 9 7 The ABS warning lamp will light to indicate system problems If the warning lamp does not light with the key on or if the computer will not go into a diagnostic mode you may have to make some voltage tests at a diagnostic connector Almost all diagnostic connectors have a ground terminal that is used for one or more test modes Use a voltmeter to check the voltage drop between the diagnostic ground terminal and the battery negative terminal High ground resistance or an open circuit can keep the computer out of the self test mode and may be a clue to other system problems Various other terminals on the diagnostic connector may have other levels of voltage applied to them at different times Some may have battery system voltage present under certain condi tions Others may have 5 volts 7 volts or a variable voltage applied for specific test conditions Self test programs and diagnostic modes operate differently on different vehicles but all pro vide the same basic kind of information Most ABS computers with any kind of self test capabil ity allow a scan tool or special tester to read system trouble codes The following paragraphs outline the common features and principles of trouble code diagnosis a S SERVICE TIP Dirty or dam
62. ures are similar it is important to check manufacturers instructions for spe cific years and models The bleeding sequence usually begins with the wheel farthest from the master cylinder but different sequences are specified by different manufacturers Delco Moraine III Before bleeding the wheel brakes turn the ignition off and pump the brake pedal thirty to forty times to exhaust accumulator pressure Leave the ignition off and the accu mulator depressurized while manually bleeding the front brakes Bleed the RF caliper first then the LF caliper To bleed the rear brakes turn the ignition on to let the pump recharge the accumulator Have an assistant press the brake pedal slowly while you open the RR bleeder screw Do not press the brake pedal to the limit of its travel Doing so discharges the accumulator too fast Hold the bleeder screw open for about 15 seconds while your assistant maintains pedal pres sure Then close the bleeder screw release pedal pressure refill the fluid reservoir and repeat the procedure at the LR wheel Delphi Chassis Delco Moraine ABS VI To bleed the ABS VI system the pistons in the front and rear modulators must be in their upper positions to unseat the check balls in the hydraulic circuits GM recommends using a scan tool with bidirectional control to do this Although a scan tool makes the job faster and easier the pistons can be positioned manually To manually position the modulator pistons start t

9 General ABS Service

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