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1999-2000 Medium Duty LPG Service Manual Supplement

1. eeeseseeeeeeeeseeeeee esee KNAK nennen namen n NNSA EANAN ANNENS enin nn nnns 5 Low Pressure Regulator LPR eeeeeelesessieeeeeeeeei eren en nennen ennt nnnnn 5 Fuel Mixer nere Uere ERE 6 Alternative Fuel Engine Control Unit AF ECU eese 6 Low Pressure Lock off EPL 1 1er err eree rct trernereIeerr I IIirRus 6 Control Soleroids iie Iii Iu ENAN a E NARAN aa 6 Regulator Control Valve RCV llseeeseeesieeeesieseeennn nien nh nnn nnns rnnt nn nnn 6 Diagnostic Information and Procedures eese eene enne nnn nnn 7 Eig rie 7 Engine Controls Schematic seeeeeeeeseeeeeeesee enne nennen nnne nnn nnn nnns 8 AF ECU Connector End Views ecce nn nnn nnn nnn 10 Alternative Fuels AF Powertrain OBD System Check 12 Malfunction Indicator Lamp Circuit ceeeeeeereeee enne nnne 15 AF Fuel System Diagnosis eeeeeeeeeeeeeeeeeen eene nennen nnne nnn nnn nnn 18 AF Fuel Control System Diagnosis eese nnne nnn 23 DTC 14 ECT Sensor Circuit High Voltage eeeeeeeeereneee nnne nnn 30 DTC 15 ECT Sensor Circuit Low Voltage eere 34 DTC 16 ECT Excessive Time to Closed Loop ee
2. Dmm oes vm imer ion ge imate Fu i EGN LIP Sio Sigra low Module PCM Sina d Unit AF EGU i P ar 2 SAO BLU IIIT AW e BLU binc MDC 1653 PNK HO2S Mou eoe coos PPL WHT PNK TAN WHT fonition Rower Heated Oxygen Signal Sensor HO2S 1 Bank 1 Ground HO2S Bank 2 lt Sensor 1 Circuit Description 40 C 104 F and the mass air flow is above 17 g s for at least 100s The PCM supplies a bias voltage of about 0 45 volt e The HO2S sensor showed ro rich lean activity between the HO2S high and HO2S low circuits The for longer than 15 seconds Heated Oxygen Sensor HO2S Bank 1 Sensor 1 varies the voltage within the range of about 1 0 Action Taken When the DTC Sets 1000 mV volt if the exhaust is rich down to about 0 1 100 mV volt if the exhaust is lean The MIL will be turned on after 2 consecutive trips The sensor is like an open circuit and produces no with test failures The system will operate in Open voltage when it is below 360 C 600 F This will Loop if any DTC of the second HO2S Bank 2 result in Open Loop operation Sensor 1 is set DTC 63 64 or 65 The HO2S heater provides for a faster sensor warm up which allows the sensor to become active in a Conditions for Clearing the MIL DTC shorter period of time and remain active during a long extended idle The ECU turns the MIL off after 3 consecutive DTC 42 determines if the HO2S or the HO2S circuit driving trips without a fault conditio
3. The AF fuel control system is operating normally Refer to Symptoms Diagnosis 1 Disconnect all test equipment 2 If you were sent to this routine by another diagnostic chart return to the previous diagnostic procedure System OK Is the action complete Go to Step 36 a System OK m 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 29 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 14 ECT Sensor Circuit High Voltage Alternative Fuel Engine Control Unit AF ECU 1 l i ECT 1 1 Sensor Signal 4 wee ee ee ee eee ee ee C001 BLU Circuit Description The Engine Coolant Temperature ECT sensor is a thermo resistor that controls the signal voltage to the PCM The PCM applies a voltage on the 5 volt reference circuit to the sensor When the engine is cold the sensor resistance is high therefore the PCM senses a high voltage signal and the PCM indicates a low coolant temperature As the engine warms the sensor resistance becomes less and the voltage drops indicating high coolant temperature At normal engine operating temperature 85 C to 95 C the voltage measures about 1 5 to 2 0 volts The AF ECU receives coolant temperature directly from the ECT signal circuit This is a type B DTC Conditions for Setting the DTC The following conditions will set the DTC e The engine has been running longer than 5 seconds at intake air temperatures greater than 0 C 32 F or fe
4. Connect a test lamp between the MAF sensor ignition feed and ground circuits at the MAF sensor harness connector Is the test lamp on Connect a test lamp between the MAF sensor ignition feed circuit and the battery ground Is the test lamp on Check for the following conditions Objects blocking the throttle body inlet screen e Vacuum leaks in the intake manifold e Vacuum leaks in the throttle body Vacuum leaks in the EGR flange and pipes The crankshaft ventilation valve for being faulty missing or incorrectly installed 2 If a problem is found repair as necessary Was a problem found Go to Step 21 Go to Step 11 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Step Action Values Yes No Go to Step 21 Go to Step 19 1 Check for a poor connection at the MAF sensor 2 If a poor connection is found replace the faulty Go to Step 21 Go to Step 20 Go to Step 21 terminal Did you find a poor connection Check the MAF signal circuit between the PCM and the MAF sensor for an open short to ground or a short to the MAF sensor ground circuit If the MAF signal circuit is open or shorted repair as necessary Refer to Wiring Repairs in Engine Electrical Was the MAF signal circuit open or shorted Locate the open in the ground circuit to the MAF sensor Repair the open in the ground circuit to the MAF sensor Is the action complete The MAF sensor circuit to the ECU
5. vao Ye Ns Was the Alternative Fuels AF Powertrain On Board Diagnostic OBD System Check performed 1 Install a scan tool 2 Start the engine 3 With the engine idling monitor the MAF frequency display on the scan tool Is the MAF frequency above the specified value 1 Backprobe the MAF circuit in the ECU connector using a DVOM set to read frequency 2 Monitor the MAF circuit frequency on the DVOM with the engine idling Is the MAF frequency above the specified value 1 Operate the vehicle within the conditions for setting this DTC as specified in the supporting text 2 Check to see if the MIL light illuminates Did the MIL illuminate Turn OFF the engine Disconnect ECU connector C003 Turn the ignition ON leaving the engine OFF Monitor the MAF frequency display on the DVOM with the engine idling Is the MAF frequency above the specified value Go to AF Powertrain OBD System 11 kHz Go to Step 7 Go to Step 3 10 39 kHz Go to Step 7 Go to Step 4 Diagnostic Go to Step 5 Aids 10 39 kHz Go to Step 7 Go to Step 6 Go to 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 59 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Value s 1 Check for a poor connection at the ECU connector 2 If a poor connection is found replace the faulty terminal ves m Go to Step 14 Go to Step 12 Go to Step 8 Go to Step 9 Go to Step 14 Go to Step 9 Go
6. Service Manual Liquefied Petroleum Gas LPG Fuel System For 1999 and 2000 GM 7 4L Medium Duty Chassis Website 5 29 03 Liquefied Petroleum Gas LPG Fuel System For 1999 and 2000 GM 7 4L Medium Duty Chassis This manual provides information on the diagnosis the service procedures the adjustments and the specifications for the Liquefied Petroleum Gas LPG Fuel System as used on the 1999 and 2000 GM 7 4L Medium Duty Chassis This manual is a supplement to be used with the 1999 and 2000 GM MD Truck service manual All information illustrations and specifications in this manual are based on the latest product information available at the time of publication IMPCO reserves the right to make changes at any time without notice No part of this manual may be reproduced stored in any retrieval system or transmitted in any form or by any means including but not limited to electronic mechanical photocopying and recording without prior written permission of IMPCO Technologies Inc 1999 IMPCO TECHNOLOGIES INC 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 2 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM CONTENTS Vehicle Application 5 eee eee ed cet ccctedacqccdieatsecceeactucdeeeteccteseceacdeeete 5 Propane Fuel System Warning eeeeeeeeeeeeeeeeee eene nennen nn nnn nn nnn nn nnne nn nnn 5 General Description cheer Rene IPM 5 Propane Fuel System
7. Check the generator output voltage If all procedures have been completed and no malfunction has been found review and inspect the following items Visually and physically inspect all electrical connections within the suspected circuit and or systems Check the scan tool data 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 100 IMPCO PROPANE FUEL SYSTEM Poor Fuel Economy Gwds An DEFINITION Fuel economy as measured by an actual road test is noticeably lower than expected Also the economy is noticeably lower than it was on this vehicle at one time as previously shown by an actual road test Preliminary Checks Sensor Checks Ignition System Checks Cooling System Checks Website 5 29 03 Refer to mportant Preliminary Checks Check the air cleaner element filter for dirt or being plugged Visually Physically check the vacuum hoses for splits kinks and proper connections as shown on the Vehicle Emission Control Label Check the owner s driving habits for the following items Is the A C ON full time Defroster mode ON Is there excessive idling or stop and go driving Are the tires at the correct air pressure Are excessively heavy loads being carried Is their often rapid acceleration Suggest to the owner to fill the fuel tank and to recheck the fuel economy Suggest to the driver to refer to Important Facts on Fuel Economy in the GM MD Owner s Manual Check the Engine Coo
8. Engine Controls Schematic cor J Cee o2 aree REI E m pi IDE CONTROL SOLENOD C POWER LE CONTROL SOLENOD C CO CAE CONTI Soubvore X 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 8 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Aj FUEL Pew Ate eDmOR Ge B s ne out Biz WT Ja PUEL 1 our LPL POWER UNDERHOOO LPL GND UNDERHOOC LOW PRESSURE LOCK OF LAL socom SM we io om Lt Powe non UNDERBOUY LPL GND os Wwe mr MONS SAL TUI m oo Lela R OUY LOW an PRESSURE LOCK OFF LPL MP 3V AFRE 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 9 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM AF ECU Connector End Views Blue C001 32 Pin Connector End View Connector Part e 12129025 Wire Circuit m c no mee NotUsed Eo a t ue 10 B 5 MAP 5V Reference 07 GRY 10 BLK 407 MAP Sensor Ground Ld NoUsd i5 YE 459 EGTSensorSigna Piero We sed not sed 26 DK GRN 428 ETC Solenoid Ground WHT ar NWaUsed 28 BLK WHT 905 Underbody LPL Ground 29 _ NotUsed 30 BLK 901 Underhood LPL Ground 3132 NotUsed AN T T RY LK YEL 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 10 Website 5 29 03 Red C002 32 Pin Connector End View Connector Part e 12129025 Wire sie jenes Bn
9. Go to Step 7 Go to Step 4 Turn the ignition OFF Disconnect ECU connector C001 Turn the ignition ON Observe the H02S sensor reading on the scan tool 200 mV Does the scan tool indicate the bank 2 HO2S 1 voltage less than the specified value Go to Step 14 Go to Step 5 Remove the jumper wire Using a DVOM measure the voltage between the bank 2 HO2S 1 high signal circuit and a 375 mV to known good ground 525 mV Is the voltage within the specified range Go to Step 6 Go to Step 8 1 Disconnect the PCM connector 2 Using a DVOM check for continuity of the bank 2 HO2S 1 signal low circuit between the PCM and the HO2S connector 3 Check the bank 2 HO2S 1 low circuit for a short to ignition power or ground Was a problem found Go to Step 17 Goto Step 16 1 Remove the jumper wire 2 Using a DVOM measure the voltage between the bank 2 HO2S 1 high signal circuit and a 375 mV to known good ground 525 mV Is the voltage within the specified range Go to Step 9 Go to Step 8 Disconnect the PCM connector Using a DVOM check for continuity of the bank 2 HO2S 1 signal high circuit between the PCM and the HO2S connector Check the bank 2 HO2S 1 high circuit for a short to ignition power or ground Was a problem found Go to Step 17 Go to Step 16 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 81 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM ration vewis Ye We Check for a poor terminal c
10. IMPCO PROPANE FUEL SYSTEM Diagnostic Aids Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure A scan tool indicates the temperature of the ambient air entering the throttle body The air temperature should read very close to the temperature of the outside air The air temperature should rise gradually as the engine warms up and the underhood temperature increases Check for poor connections at the ECU and IAT sensor by wiggling the connector gently and monitoring the IAT voltage on a DVOM connected to the ECU connector If the voltage waivers repair the connector that caused the waiver Also a sensor may become skewed or mis scaled The Temperature vs Resistance value table will help to detect a skewed sensor Refer to Temperature vs Resistance Test Description The numbers below refer to the step numbers on the diagnostic table Important Use the same diagnostic test equipment for all of the measurements 3 If the IAT sensor circuit voltage measures greater than 4 88 volts the conditions for the DTC are still present and the problem is not intermittent 4 With the ECU connector disconnected and the voltage still present this eliminates the ECU as the possible cause of the fault DTC 25 IAT Sensor Circuit High Voltage Sep Ado Veo Yes Ne Was the Alternative Fuels AF Powertrain On Board Diagnostic OBD System Check performed 1 Connect the scan
11. When the vehicle s operator initially turns on the ignition the MIL will illuminate for 2 seconds If no Diagnostic Trouble Codes DTCs are stored the Powertrain Control Module PCM turns off the MIL The PCM controls the MIL providing a ground path through the MIL control circuit in order to turn on the MIL The MIL control circuit is routed through the Alternative Fuel Electronic Control Unit AF ECU to give the ECU the ability to turn on the MIL if an AF system DTC is set Diagnostic Aids An open gauge fuse will cause the entire IP cluster to be inoperative Check any circuitry that is suspected of causing an intermittent condition for the following conditions e Backed out terminals Improper mating Broken locks Improperly formed or damaged terminals Poor terminal wiring connections Physical damage to the wiring harness IMPCO PROPANE FUEL SYSTEM Test Description The numbers below refer to the step numbers on the diagnostic table 1 The powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data with the scan tool if applicable This creates an electronic copy of the data when the fault occurred The information is then stored in the scan tool for later reference 3 Ifthe MIL illuminates but does NOT turn off after 2 seconds the PCM may have incorrect software 4 Ifthe engine fails to start and the MIL is inoperative then the faul
12. body to monitor the temperature of the air entering the throttle body The PCM applies 5 volts to the sensor on a 5 volt reference circuit When the air is cool resistance in the sensor measures high and the ECU senses a high voltage signal If the air is warm the sensor resistance measures low and the ECU senses a low voltage signal This DTC is a type B DTC Conditions for Setting the DTC The following conditions will set the DTC All of the conditions below must be met for at least 10 seconds e Vehicle speed must be less than 1 mph e Air flow must be less than 250 grams per second e AT voltage is greater than 4 88 volts e f ECT at start is greater than 0 C the DTC will test at 100 seconds of run time or e f ECT at start is less than 0 C the DTC will test at 600 seconds of run time Action Taken When the DTC Sets The ECU sets the DTC 25 after 2 consecutive driving cycles with the fault active Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F from the start up coolant temperature and the engine coolant temperature exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 44 Website 5 29 03
13. contamination by the liquid leak detector PROPANE FUEL FILTER REPLACEMENT Removal Procedure 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief Disconnect the negative battery cable Disconnect the fuel inlet line from the filter Remove the nut retaining the filter clamp Unscrew the filter from the electric lock off o9 RON Installation Procedure Coat the male pipe threads with a liquid thread sealant compound Install and tighten the filter into the lock off assembly Install and secure the filter clamp and nut Connect the fuel inlet line to the filter and tighten Open manual shut off valve Start the vehicle and leak check the propane fuel System at each serviced fitting m OOT Go LOW PRESSURE LOCK OFF LPL REPLACEMENT UNDERBODY Removal Procedure 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief 2 Disconnect the negative battery cable 3 Remove the propane fuel filter Refer to Propane Fuel Filter Replacement 4 Disconnect the electric lock off solenoid electrical connector 5 Disconnect the fuel line 6 Remove the two 2 electric lock off solenoid mounting bolts 7 Remove the lock off from the bracket 8 Remove the elbow fitting from the fuel outlet port Installation Procedure Important e Do not use Teflon tape on any fuel fitting Use a liquid pipe thread sealant when installing fittings Instal
14. 18 Go to Step 8 Go to Step 14 Go to Step 10 Go to Step 9 Go to Step 11 Goto Step 12 Goto Step 14 Go to MIL Circuit Diagnosis in the GM MD Service Disconnect ECU connector C002 2 Using a scan tool command the MIL on and off Does the MIL operate as commanded Disconnect ECU connector C002 2 Check for continuity of the MIL circuit between connectors C002 and C009 Is there continuity Is the MIL continuously illuminated 1 Disconnect connector C009 2 Using a scan tool command the MIL on and off Does the MIL operate as commanded Go to Step 11 Repair the short to ground in the MIL control circuit Is the action complete 1 Check the PCM ignition power battery power and ground circuits for shorts and opens 2 Check the ECU ignition power battery power and ground circuits for shorts and opens Go to Step 18 Diagnostic by Symptom Was as problem found Go to Step 17 Hard Start Go to Step 17 Goto Step 15 Go to Step 17 Goto Step 16 Go to Step 18 Check for faulty ECU connections Was a problem found Check for faulty connections at connector C009 Was a problem found Replace the ECU Is the action complete Repair as necessary Go to Step The circuit between connectors C009 and C002 is shorted to power or ground Repair the circuit as necessary Is the action complete Go to Step 18 Is the action complete 1999 2000 GM Medium Duty Chassis Service Manual Sup
15. 29 03 IMPCO PROPANE FUEL SYSTEM 3 This step determines if the ECU is receiving the Crankshaft Position sensor pulses 6 This step checks the CKP sensor signal circuit for any unusual loading conditions If the ECU is not receiving a signal and no circuit faults can be found The PCM is not 2 This step determines if the DTC 41 is the outputting a tachometer signal and should result of a hard failure or an intermittent be diagnosed condition Test Description The numbers below refer to the step numbers on the diagnostic table DTC 41 CKP Sensor Circuit Performance Step Ado Vas Ye No O Was the Alternative Fuels AF Powertrain On Board Go to AF Diagnostic OBD System Check performed Powertrain OBD System Go to Step 2 EIS Go to Diagnostic Aids Go to Step 3 Go to Step 5 Go to Step 4 Start the vehicle Does the vehicle start and continue to run Turn OFF the ignition Backprobe CKP sensor circuit at ECU connector C003 Connect a DVOM set to read AC voltage between the CKP sensor signal circuit and a known good ground Crank the engine Is voltage detected while the engine is cranking 1 Turn OFF the ignition 2 Disconnect the PCM connector 3 Disconnect ECU connector C003 1 Clear the DTC 2 Operate the vehicle within the conditions for setting this DTC as specified in the supporting text 3 Check to see if the MIL still illuminates Go to Diagnostic Did the d
16. 9 Go to Step 13 Replace the ECU Refer to ECU Replacement Is the action complete Go to Step 16 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 31 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Turn the ignition OFF Disconnect the ECT sensor connector Jumper the ECT sensor harness terminals together Turn the ignition ON Observe the engine coolant temperature parameter on the scan tool Is the ECT sensor at the specified value Jumper the ECT sensor signal circuit to a known good ground Is the ECT sensor at the specified value The DTC is intermittent If no additional DTCs were stored refer to the Diagnostic Aids If any additional DTCs are stored refer to those tables Are any additional DTCs set Inspect the ECT sensor connector and the PCM connector for the proper connection Was a problem found Check the ECT sensor ground circuit for an open between the ECT sensor and the PCM Was a problem found Check the ECT sensor signal circuit for an open between the ECT sensor and the PCM Was a problem found Repair the circuit as necessary Is the repair complete Replace the ECT sensor Is the replacement complete Replace the PCM Important If the PCM is faulty reprogram the PCM Refer to PCM Replacement Programming The 7 4L LPG fuel system requires a unique PCM software calibration Is the replacement complete 1 Operate the vehicle within the conditions for se
17. Check the EGR valve operation for being open all the time Refer to EGR System Diagnosis in the GM MD Service Manual 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 98 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Lack of Power Sluggishness or Sponginess DEFINITION The engine delivers less than expected power There is little or no increase in speed when partially applying the accelerator pedal Preliminary Checks Refer to Symptoms Refer to the Alternative Fuel AF Powertrain OBD System Check Search for service bulletins Compare the customer s vehicle with a similar unit Make sure the customer has an actual problem Do not compare the power output of the vehicle operating on LPG to a vehicle operating gasoline as the fuels do have different drive feel characteristics Remove the air filter and check for dirt or restriction Check the transmission shift pattern and the downshift operation Fuel System Checks Check for a restricted fuel filter contaminated fuel or improper fuel pressure Refer to AF Fuel System Diagnosis Check for the proper ignition output voltage with the spark tester J 26792 or the equivalent Check for proper installation of the mixer module assembly Check all air inlet ducts for condition and proper installation Check for fuel leaks between the LPR and the mixer Verify proper operation of the regulator control valve RCV Verify that the LPG tank manual shut off valve is fully o
18. Checks e Check the Engine Coolant Temperature ECT sensor with the scan tool Compare the engine coolant temperature with the ambient air temperature on a cold engine IF the coolant temperature reading is more than 5 degrees greater or less than the ambient air temperature on a cold engine check for high resistance in the coolant sensor circuit Refer to DTC P0118 ECT Sensor Circuit High Voltage or DTC P1115 ECT Sensor CKT Intermittent High Voltage in the GM MD Service Manual e Check the Crankshaft Position Sensor CKP e Check the Mass Air Flow MAF sensor Fuel System Checks Important A closed LPG manual fuel shut off valve will create an extended crank OR no start condition e Check the fuel pump relay for proper operation The fuel pump relay circuit supplies a voltage signal to the AF system ECU and lock off valves Refer to Fuel Pump Circuit Diagnosis in the GM MD Service Manual Verify proper operation of the low pressure lock off solenoids Verify proper operation of the fuel control solenoid Verify proper operation of the ETC control solenoid Verify proper operation of the idle control solenoids Check for air intake system leakage between the mixer and the throttle body Check the fuel system pressures Refer to the AF Fuel System Diagnosis Check mixer module assembly for proper installation and leakage 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 94 Website 5 29 03 IMPCO PROPANE FUEL
19. Control Engine Control Unit AF ECU B2 1 Circuit Signal Module PCM Signal C2 BLU mE C001 BLU 1667 C005 Sensor 1 Ignition Power HO2S B2 1 Signal Ground HO2S Bank 1 Sensor 1 Circuit Description The ECU supplies a voltage of about 0 45 volt 450 mV between the HO2S high and HO2S low circuits The Heated Oxygen Sensor HO2S Bank 2 Sensor 1 varies the voltage within the range of about 1 0 volt 1000 mV if the exhaust is rich down to about 0 10 volt 100 mV if the exhaust is lean The sensor is like an open circuit and produces no voltage when it is below 360 C 600 F This will result in Open Loop operation The HO2S heater provides for a faster sensor warm up which allows the sensor to become active in a shorter period of time and remain active during a long extended idle DTC 63 determines if the HO2S at the HO2S circuit has developed an open This DTC is a type B DTC Conditions for Setting the DTC e Engine run time is greater than 120 seconds e Engine is running at greater than 500 RPM Heated Oxygen Sensor HO2S 1 Bank 2 e The oxygen sensor has been warm for at least 120 seconds The oxygen sensor is determined to be warm by the ECU if ECT is greater than 40 C 104 F and the mass air flow above 17 g s for at least 120s e The HO2S sensor showed no rich lean activity for longer than 15 seconds Action Taken When the DTC Sets The MIL will be turned on after 2 cons
20. Duty Chassis Service Manual Supplement Page 37 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Diagnostic Aids Improperly formed or damaged terminals Poor terminal to wire connection and Always diagnose ANY PCM codes that are present Damaged harness before beginning this diagnostic procedure e The intermittent test If the connections and the When a DTC 16 sets a skewed ECT sensor or an harness check OK monitor a DVOM connected engine thermostat that does not operate correctly is to the ECU terminal while moving the related indicated connectors and the wiring harness If the failure A poor connection a rubbed through wire insulation is induced the voltage reading changes This or a wire broken inside the insulation may cause an may help isolate the location of the malfunction intermittent Test Description Check for the following conditions e A poor connection or damaged harness Inspect The numbers below refer to the step numbers on the the ECU harness connector for the following diagnostic table conditions Backed out terminals 6 This test checks the engine warm up rate Improper mating 8 This test checks the coolant sensor reading Broken locks and the actual coolant temperature DTC 16 ECT Excessive Time to Closed Loop Step Action Value s Was the Alternative Fuels AF Powertrain On Board Diagnostic OBD System Check performed Go to AF Powertrain OBD System heck Go to Step 2 eee Go t
21. E a a N e A 9 28 BK S Notus ses Mousa 1 N zu m ou alala E Qm oj eS ls o IMPCO PROPANE FUEL SYSTEM Clear C003 32 Pin Connector End View Connector Part e 12129025 Wire en jene RECO NEN i21 TACH Input Signal BR Ce 489 Vehicle Speed Sensor EL Input Signal 4 NotUsed Oo A 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 11 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Alternative Fuels AF Powertrain OBD System Check The above chart is exarnpie of the timing sequence to flash DTC 12 Circuit Description The On Board Diagnostic OBD System Check is an organized approach to identifying a problem created by a control module system malfunction The OBD is the starting point for any driveability concern diagnosis The OBD directs the service technician to the next logical step in diagnosing the concern This system check will address possible faults in two separate control module systems To avoid unnecessary diagnostic time follow the system check carefully Perform this check ONLY if there is a driveability complaint or if you have been sent to this system check from another section in the service information Understanding the table properly reduces the diagnostic time Proper use of the OBD helps prevent the unnecessary replacement of good parts Diagnostic Aids Important Do not clear DTCs unless directed by a
22. Go to Step 9 Goto Step 5 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 75 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Step Action Values Disconnect the PCM connector Using a DVOM check for continuity of the bank 1 HO2S 1 signal high circuit between the PCM ECU and the HO2S connector Check the bank 1 HO2S 1 high circuit for a short to voltage or ground Check the bank 1 HO2S 1 low circuit for a short to voltage or ground Was a problem found ves Ne Go to Step 12 Go to Step 11 Go to Step 12 Goto Step 7 Go to Step 14 AN Check for a poor terminal connection at the bank 1 HO2S 1 connector Check all circuits for loose terminal tension Install a test lamp between the bank 1 HO2S 1 heater high and low circuits the test lamp should illuminate Was a problem found Replace the bank 1 HO2S 1 Is the action complete Check for a poor connection at the ECU Go to Step 12 Go to Step 10 Go to Step 14 Go to Step 12 Go to Step 13 Go to Step 14 Go to Step 14 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 76 Was a problem found Replace the ECU Refer to ECU Replacement Is the action complete Check for a faulty or loose connection at the PCM connector Was a problem found Repair the circuit as necessary Is the action complete Replace the PCM Important If the PCM is faulty reprogram the PCM Refer to PCM Replacement Prog
23. Medium Duty Chassis Service Manual Supplement Page 34 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM open in the 5 volt reference circuit or the sensor Test Description ground circuit results in a DTC 15 The numbers below refer to the step numbers on the Use the Temperature vs Resistance Value Table to diagnostic table test the coolant sensor at various temperature levels in order to evaluate the possibility of a skewed mis 3 If the fault is present the engine coolant scaled sensor A skewed sensor could result in temperature voltage at the ECU measures poor driveability complaints Refer to Temperature less than 0 019 volts If the PCM is reading vs Resistance below 190 C 282 F and the ECU voltage is above 0 019 refer to the base vehicle service manual DTC 15 ECT Sensor Circuit Low Voltage Sep Ado wo Yes No Was the Alternative Fuels AF Powertrain On Board Go to AF Diagnostic OBD System Check performed Powertrain OBD System heck Go to Step 2 xiu 1 Connect the scan tool Go to DTC 2 Start the engine P0117 3 Observe the ECT sensor reading ECT Sensor f n Circuit Low IOS SEE Voltage in the GM MD Does the scan tool display the ECT sensor reading Service GREATER than the specified value Manual Go to Step 3 Using a DVOM backprobe the ECT sensor signal in the ECU connector 0 019 V Does the DVOM display the ECT sensor signal LESS ifi than the specified value Go to Step 4 Go to St
24. Sensor 1 sensor electrical connector 2 Observe the H02S sensor reading on the scan 350 mV to tool 550 mV Does the scan tool indicate the bank 1 HO2S 1 voltage is within the specified range Go to Step 6 Go to Step 4 Turn the ignition OFF Disconnect ECU connector C001 Turn the ignition ON Observe the H02S sensor reading on the scan 350 mV to tool Does the scan tool indicate the bank 1 HO2S 1 voltage within the specified range Goto Step 9 Goto Step 5 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 71 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Step Acion Vae 1 Disconnect the PCM connector 2 Using a DVOM check for continuity of the bank 1 HO2S 1 signal high circuit between the PCM ECU and the HO2S connector 3 Check the bank 1 HO2S 1 high circuit for a short to voltage or ground ves Ne Go to Step 12 Goto Step 11 Go to Step 12 Go to Step 7 Go to Step 14 Was a problem found 1 Check for a poor terminal connection at the bank 1 HO2S 1 connector Check all circuits for loose terminal tension 2 Install a test lamp between the bank 1 HO2S 1 heater high and low circuits the test lamp should illuminate Was a problem found Replace the bank 1 HO2S 1 Is the action complete Check for a poor connection at the ECU Go to Step 12 Go to Step 10 Go to Step 14 Go to Step 12 Go to Step 13 Go to Step 14 Go to
25. Step 14 H 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 72 Was a problem found Replace the ECU Refer to ECU Replacement Is the action complete Check for a faulty or loose connection at the PCM connector Was a problem found Repair the circuit as necessary Is the action complete Replace the PCM Important If the PCM is faulty reprogram the PCM Refer to PCM Replacement Programming The 7 4L LPG fuel system requires a unique PCM software calibration Is the action complete The DTC is intermittent Are there any Powertrain Go to the DTCs displayed that have not been diagnosed applicable Go to Powertrain Diagnostic DTC table Aids Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Sep Adon 7 Vawj Yes Ne Bring the engine up to normal operating temperature Run the engine above the specified value for at least 4 minutes Turn OFF the engine and the ignition for at least 1500 RPM 10 seconds Run the engine above the specified value for at least 4 minutes second time Did the MIL illuminate Go to Step 2 osse y 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 73 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 45 HO2S Circuit High Voltage Bank 1 Sensor 1 1665 C006 HO2S Bank 2 Sensor 1 1665 PPL WHT 1665 Ignition Power Ground HO2S Bank 2 Sensor 1 Circuit Description The ECU supplies a voltage of about 0 45 v
26. Step 28 Inspect the fuel hose connection between the LPR Was a problem found and repaired Go to Step 30 Go to Step 22 and the mixer assembly for damage or leakage 1 Connect a 0 5 psi gauge to the primary test port of the low pressure regulator LPR 2 Crank the engine and observe the pressure 1 psi 1999 reading for the LPR primary pressure or 4 psi 2000 Is fuel pressure present above the specified value Go to Step 26 Go to Step 13 Turn OFF the ignition Disconnect the underhood LPL connector Install a test light between the pins of the LPL connector Crank the engine The test light should illuminate Does the test light illuminate Go to Step 14 Go to Step 16 Using a DVOM check the resistance of the low pressure lock off LPL 6 2 0 100 Is the resistance within the specified range Go to Step 15 Go to Step 27 1 Turn the ignition OFF 2 Close the manual shut off valve on the LPG tank CAUTION When disconnecting LPG fuel lines liquid LPG may be present Perform this step in a well ventilated area 3 Loosen the fuel inlet hose fitting at the inlet of the underhood LPL TIT Was fuel present when the fitting was loosened Go to Step 27 Go to Step 17 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 20 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM value s Yes No Turn OFF the ignition Connect the test light to chassis ground and probe pin A of the LPL conne
27. Vacuum or crankcase leaks can cause a lean condition or possibly a high idle e If the above check out okay the problem may be a faulty heated sensor e A faulty HO2S Bank 1 Sensor 1 heater or heater circuit With the ignition switch on but the engine off the HO2S Bank 1 Sensor 1 voltage displayed on a scan tool should gradually drop to below 0 150 volt indicating that the heater works properly If not disconnect the HO2S Bank 1 Sensor 1 and connect a test lamp between the terminals C and D f the test lamp does not light repair the open in the HO2S Bank 1 Sensor 1 ground circuit or the HO2S Bank 1 Sensor 1 ignition feed circuit If the test lamp lights replace the HO2S Bank 1 Sensor 1 The intermittent test With a scan tool monitor the HO2S Bank 1 sensor 1 signal voltage while moving the related connectors and the wiring harness with a warm engine running at part throttle in closed loop If the failure is induced the HO2S Bank 1 Sensor 1 signal voltage reading changes from its normal fluctuating voltage above 600 mV and below 300 mV to a fixed value around 450 mV This may help isolate the location of the malfunction Never solder the HO2S wires For proper wire and connector repair refer to Wiring Repairs in Engine Electrical Test Description The number s below refer to the step numbers on the diagnostic table 2 This test will indicate if the fault is still present if the fault is
28. body The PCM applies 5 volts to the sensor on a 5 volt reference circuit When the air is cool resistance in the sensor measures high and the ECU senses a high voltage signal If the air is warm the sensor resistance measures low and the ECU senses a low voltage signal This DTC is a type B DTC Conditions for Setting the DTC The following conditions will set the DTC e Vehicle speed is greater than 1 mph e Engine run time is greater than 100 seconds e IAT voltage is below 0 019 volts Action Taken When the DTC Sets The ECU sets the DTC 23 after 2 consecutive driving cycles with the fault active Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F from the start up coolant temperature and the engine coolant temperature exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used Diagnostic Aids Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure A scan tool indicates the temperature of the ambient air entering the throttle body The air temperature should read very close to the temperature of the outside air The air temperature should rise gradually as the engine warms up and the underhood temperature increases Check for poor connectio
29. camshaft lobes Broken or weak valve springs Check the intake and exhaust manifold passages for casting flash Fuel System Checks Check the fuel system plugged fuel filter low fuel pressure etc Refer to AF Fuel System Diagnosis Check the condition of the wiring to the low pressure lock off solenoid Additional Check Check for Electromagnetic Interference EMI EMI on the reference circuit can cause a missing condition Monitoring the engine RPM with a scan tool can detect an EMI A sudden increase in the RPM with little change in the actual engine RPM indicates EMI is present If the problem exists check the routing of the secondary wires and the ground circuit 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 96 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Hesitation Sag Stumble We Am DEFINITION The vehicle has a momentary lack of response when depressing the accelerator The condition can occur at any vehicle speed The condition is usually most severe when trying to make the vehicle move as from a stop sign The condition may cause the engine to stall if i s severe enough Preliminary Checks Refer to Important Preliminary Checks Fuel System Checks Check the fuel pressure Refer to AF Fuel System Diagnosis Check for low fuel pressure during a moderate or full throttle acceleration If the fuel pressure drops below specification there is possibly a faulty low pressure regulator or a restric
30. check the test port plugs Is the action complete Replace the lock off Refer to Low Pressure Lock off LPL Replacement Is the action complete Go to Step 30 Go to Step 30 a Website 5 29 03 AF Fuel Control System Diagnosis IMPCO PROPANE FUEL SYSTEM Fuel Pump Relay GRY 29 C Fuel Control Solenoid FCS D YEL 911 DK GRN WHT Purge Control Solenoid PPLAWHT 1665 C001 BLU RED Fuel Control System Components The main components of the fuel control system are e The alternative fuel engine control unit AF ECU e The low pressure regulator LPR e The regulator control valve RCV The fuel mixer The Fuel Control Solenoid FCS The Idle Control Solenoid ICS The ETC Solenoid Fuel Control System Operation The AF ECU receives information from various engine sensors in order to control the fuel and idle control valves to maintain closed loop operation During normal operation the ECU commands a duty cycle to the fuel control solenoid FCS The FCS modulates air valve vacuum and atmospheric pressure on top of the secondary diaphragm of the LPR By controlling the pressure on top of the LPR secondary diaphragm the ECU can control the output pressure and fuel flow to the mixer A high Connector GRY 929 A Electronic Throttle Control ETC Solenoid 8 DK GRN WHT 428 DK GRN WHT C010 A Idle Control Solenoid ICS B ICS Test Connector A B
31. deposits Check the spark plug wires by connecting an ohmmeter to the ends of each wire in question If the meter reads over 30 000 ohms replace the wires Note The vehicle may be equipped with low resistance plug wires refer to MD Service Manual for proper plug wire resistance Additional Checks Important The AF system works on a fumigation principle of fuel introduction and is more sensitive to intake manifold leakage than the gasoline fuel supply system Check for vacuum leaks Vacuum leaks can cause a higher than normal idle and low throttle angle control command Check the Control Module grounds for being clean tight and in their proper locations Check the Automatic Transmission Fluid Pressure TPF manual valve indicator Refer to Transmission Fluid Pressure Switch Assembly Check the scan tool to determine if the Control Module is receiving an A C signal Refer to A C Compressor Clutch Control in the GM MD Service Manual If a problem exists with the A C ON check the A C system operation Check for EGR being ON while idling which will cause roughness stalling and hard starting Refer to EGR System Diagnosis in the GM MD Service Manual Check the battery cables and ground straps They should be clean and secure Erratic voltage may cause all sensor readings to be skewed resulting in poor idle quality Check the A C refrigerant pressure for being too high or for a faulty high pressure switch Check the Crankcase Vent
32. is then drawn from the secondary chamber of the LPR by the vacuum generated by air flowing through the mixer This vacuum signal is also used to generate lift for the mixer air valve This vacuum signal is most commonly referred to as air valve vacuum In the mixer the fuel mixes with the air entering the engine This air fuel mixture is then drawn into the engine for combustion Website 5 29 03 Primary Pressure Test Port Diagnostic Aids This procedure is intended to diagnose a vehicle operating on LPG If the vehicle will not continue to run on LPG refer to Hard Start for preliminary checks Before proceeding with this procedure verify that the vehicle has a sufficient quantity of fuel and that liquid fuel is being delivered to the LPR Also ensure that the manual shut off valve on the LPG tank is fully opened and that the excess flow valve has not been activated Tools Required e DVOM GM J 39200 Fluke 88 or equivalent Duty Cycle Monitoring Tool e MPCO Fuel System Analyzer FSA or DVOM GM J 39200 Fluke 88 or equivalent Diagnostic Scan Tool e GM Tech 2 or equivalent Pressure Gauges e Water Column Gauge Manometer GM 7333 6 or equivalent e 0 5 PSI Gauge GM 42580 or equivalent Test Description The numbers below refer to step numbers on the diagnostic table 5 This step will determine if the fuel control solenoid FCS and fuel supply system are functioning properly The vacuum on the
33. leaks can cause a lean condition or possibly a high idle e If the above check out okay the problem may be a faulty heated sensor e A faulty HO2S Bank 2 Sensor 1 heater or heater circuit With the ignition switch on but the engine off the HO2S Bank 2 Sensor 1 voltage displayed on a scan tool should gradually drop to below 0 150 volt indicating that the heater works properly If not disconnect the HO2S Bank 2 Sensor 1 and connect a test lamp between the terminals C and D f the test lamp does not light repair the open in the HO2S Bank 2 Sensor 1 ground circuit or the HO2S Bank 2 Sensor 1 ignition feed circuit If the test lamp lights replace the HO2S Bank 2 Sensor 1 e The intermittent test With a scan tool monitor the HO2S Bank 2 sensor 1 signal voltage while moving the related connectors and the wiring harness with a warm engine running at part throttle in closed loop If the failure is induced the HO2S Bank 2 Sensor 1 signal voltage reading changes from its normal fluctuating voltage above 600 mV and below 300 mV to a fixed value around 450 mV This may help isolate the location of the malfunction e Never solder the HO2S wires For proper wire and connector repair refer to Wiring Repairs in Engine Electrical Test Description The number s below refer to the step numbers on the diagnostic table 2 This test will indicate if the fault is still present if the fault is not present ope
34. mixer and restrict the airflow to reduce power The ETC solenoid is activated under normal conditions ETC Fault Mode Operation If a PCM Throttle Actuator Control TAC DTC P1514 P1515 P1516 or P1518 is detected by the AF ECU it will set DTC 31 and enter ETC Fault Mode In this mode the PCM issues a command to de energize the ETC solenoid The air valve vacuum in the mixer is vented to atmosphere causing the air valve to close and reduce airflow through the mixer to a default limit value 6 g s 9 g s This forces an idle condition The AF ECU commands the idle control solenoid ICS to fuel the engine and maintain fuel control Diagnostic Aids Always diagnose any PCM or ECU codes that are present before beginning this diagnostic procedure Refer to Important Preliminary checks and Symptom Diagnosis Charts before attempting to diagnose the AF fuel control system If the vehicle will not continue to run refer to Hard Start for preliminary checks Before proceeding with this procedure verify that the AF Fuel System Diagnosis has been performed Check for the following conditions e Loose cracked or kinked vacuum hoses e Poor connection or a damaged harness to the AF ECU FCS and ICS Poor AF ECU engine block ground Sticking mixer air valve Intake air leak between mixer and throttle body Faulty low pressure regulator LPR Exhaust leaks Fuel contamination Tools Required e DVOM GM J 39200 Fluke 88 o
35. out terminals Improper mating Broken locks Improperly formed or damaged terminals Poor terminal to wire connection and Damaged harness Test Description The numbers below refer to the step numbers on the diagnostic table 3 This step verifies battery power ignition power and ground to the AF ECM ooo o O j va s Ne Was the Alternative Fuels AF Powertrain On Board Go to AF Diagnostic OBD System Check performed Go to Step 2 Powertrain OBD System Check 2 EX Was DTC 58 retrieved from the AF ECU Go to Step 3 Go to Step 5 Check for proper connection of the ignition Go to Step 6 Go to Step 4 power and ground connections verify that the connections are clean and tight Check loose or corroded connections at the ECU connector Was a problem found and corrected Replace the ECU Refer to ECU Replacement Is the action complete Go to the applicable DTC table System OK Go to Step 7 Go to Step 2 Go to the applicable DTC table System OK Were any other DTCs set in the ECU 1 Start and run vehicle 2 Check to see if the MIL still illuminates Did the diagnostic run and pass Are any ECU or PCM DTCs displayed that have not been diagnosed Go to Step 5 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 78 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 63 HO2S Insufficient Activity Bank 2 Sensor 1 Alternative Fuel Hot in Run And Start Powertrain 1
36. output voltage Check the vacuum hoses for kinks or leaks Refer to the Vehicle Emission Control Information label on the top of the radiator Check for an Intermittent EGR problem Refer to EGR System Diagnosis in the GM MD Service Manual Check for Torque Converter Clutch TCC operation 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 107 IMPCO PROPANE FUEL SYSTEM REPAIR INSTRUCTIONS PROPANE FUEL SYSTEM PRESSURE RELIEF CAUTION The propane fuel system operates at pressures up to 312 psi To minimize the risk of fire and personal injury relieve the propane fuel system pressure where applicable before servicing the propane fuel system components To relieve propane fuel system pressure 1 Close the manual shut off valve MSV on the propane fuel tank 2 Start and run the vehicle until the engine stalls 3 Turn the ignition switch OFF Important e Residual vapor pressure will be present in the fuel system Ensure the work area is well ventilated before disconnecting any fuel line PROPANE FUEL SYSTEM LEAK TEST CAUTION Never use an open flame of any type to check for propane fuel system leaks Always inspect the propane fuel system for leaks after performing service Check for leaks at the fittings of the serviced or replaced component Use a commercially available liquid leak detector or an electronic leak detector When using both methods use the electronic leak detector first to avoid
37. tool 2 Turn the ignition ON leaving the engine OFF 3 Monitor the IAT sensor voltage Go to AF Powertrain OBD System Check pw Go to Step 2 Go to DTC P0113 IAT Sensor Circuit High Voltage in the GM MD Service 39 C 38 F Is the IAT sensor voltage at the specified value Using a DVOM backprobe the IAT sensor signal in the ECU connector Does the DVOM display the IAT sensor signal greater than the specified value 1 Turn OFF the ignition 2 Disconnect ECU connector C001 3 Turn ON the ignition Does the DVOM display the IAT sensor signal greater than the specified value 1 Disconnect the IAT sensor 2 Using a DVOM check for continuity of the IAT circuit between the IAT connector and the ECU Is there continuity Replace the ECU Refer to ECU Replacement Is the action complete Manual Go to Step 3 Go to Step 4 Go to Step 5 Go to Step 7 Go to Step 6 Go to Step 9 Go to Step 13 Go to Step 16 IN 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 45 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Step Action Vale ves m Turn OFF the engine Turn ON the ignition switch Disconnect the IAT sensor connector Jumper the IAT sensor harness terminals together Does the scan tool display the IAT sensor at the specified value Goto Step 10 Goto Step 8 Jumper the IAT sensor signal circuit to a known good ground 140 C Does the scan too
38. 1 and PCM C1 45 for an open or short to ignition power ired Was a problem found and repaired Go to Step 36 Go to Step 21 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 27 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Stepe Action Value s The ETC solenoid ignition circuit is open Locate and repair the open or short to ground in the ETC ignition power circuit from pin A ve mw Is the action complete NE EN Go to Step 25 Go to Step 36 Go to Step 29 1 Disconnect ECU connector C001 2 Turn the ignition ON leaving the engine OFF 3 Check ECU cavity C001 pin 26 for a short to power Was a problem found The ICS ignition circuit is open or shorted to ground Check the ICS ignition circuit in the ICS connector terminal A for ignition power Was a problem repaired Replace the ECU Refer to ECU Replacement Is the action complete Check the vacuum hoses between the mixer LPR and the FCS for kinks obstructions or leakage Was a problem found and repaired Check the fuel hose between the LPR and the ICS for kinks or obstructions Go to Step 36 Go to Step 27 Go to Step 31 Go to Step 36 Go to Step 30 Go to Step 31 Go to Step 36 EN 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 28 Was a problem found and repaired Replace the Idle Control Solenoid ICS Refer to Idle Control Solenoid Replacement Is the action complete In
39. 1514 P1515 P1516 or P1518 retrieved eu cem T 1 Disconnect the PCM connector J1 2 Disconnect the ECU connector C001 ground or ignition power Was a problem found and repaired 3 Check the ETC fault circuit for an open short to Go to Step 6 Go to Step 4 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 48 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Sep Adon Vawis Yes Ne Go to Step 6 Go to Step 5 Check for a poor connection at the ECU connector C001 Was a problem found and repaired Are any ECU or PCM DTOs displayed that have not been diagnosed Replace the ECU Refer to ECU Replacement Is the action complete Go to Step 6 Go to the applicable DTC Table System OK 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 49 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 34 MAP Sensor Circuit Low Voltage Exhaust Gas Reereviation EGR Vave REDIBLK 645 Manifold Absolute Pressure MAP Sensor C2 BLU Circuit Description The Manifold Absolute Pressure MAP sensor responds to changes in the intake manifold pressure vacuum A 5 volt reference is applied to the sensor A variable resistor moves in relation to manifold pressure and a voltage signal is sent back to the ECU on the 5 volt reference circuit This voltage signal varies from 1 0 1 5 volts at closed throttle high vacuum to 4 0 4 5 volts at wide open throttle low vacuum Th
40. 2 Go to Step 10 Go to Step 14 Go to Step 12 Go to Step 13 Go to Step 14 Go to Step 14 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 86 Is the action complete Check for a faulty or loose connection at the PCM connector Was a problem found Repair the circuit as necessary Is the action complete Replace the PCM Important If the PCM is faulty reprogram the PCM Refer to PCM Replacement Programming The 7 4L LPG fuel system requires a unique PCM software calibration Is the action complete The DTC is intermittent Are there any Powertrain Go to the Go to DTCs displayed that have not been diagnosed applicable Diagnostic Powertrain Aids DTC table Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Sep Adon T Vawj Yes Ne Bring the engine up to normal operating temperature Run the engine above the specified value for at least 4 minutes Turn OFF the engine and the ignition for at least 1500 RPM 10 seconds Run the engine above the specified value for at least 4 minutes second time Did the MIL illuminate So toserepest eystetmls 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 87 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 65 HO2S Circuit High Voltage Bank 2 Sensor 1 Hot in Run And Start ge es ayy Pret tO 4 HO2S EGN IP B2 1 Circuit Fuse 1 i 1 l Signal I i Breaker 1 1 1 I HO2S Bank 1 Sensor 1 ig
41. 41 and illuminate the MIL light after 1 fault has occurred Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F from the start up coolant temperature and the engine coolant temperature exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used Diagnostic Aids Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure A faulty or disconnected Mass Air Flow Sensor MAF may create a condition that will set a false DTC 41 verify operation and connection of the MAF prior to performing this diagnostic procedure Check for the following conditions e A poor connection a rubbed through wire insulation or a wire that is broken inside the insulation may cause an intermittent problem Inspect harness connectors for the following conditions Backed out terminals Improper mating Broken locks Improperly formed or damaged terminals Poor terminal to wire connection e Physical damage to the wiring harness Inspect the face of the CKP sensor for metal shavings This could result in an intermittent DTC Refer to Intermittents in the powertrain diagnostics manual 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 62 Website 5
42. 9 M9 90 co Idle Control Solenoid IMPCO PROPANE FUEL SYSTEM LOR 7 gee ee in a Tae OOD 2 Disassembly Procedure 1 Remove the LPL from the LPR 2 Remove the RCV from the LPR 3 Remove all fittings from the LPR Assembly Procedure Important e Do not use Teflon tape on any fuel fitting Use a liquid pipe thread sealant when installing fittings 1 Install all fittings to the LPR Tighten the fittings finger tight plus 1 to 2 turns 2 Install the RCV to the LPR Tighten the RCV finger tight plus 1 to 2 turns 3 Install the LPL to the LPR Tighten the LPL finger tight plus 1 to 2 turns and place the LPL in the correct position Installation Procedure Important e Do not use Teflon tape on any fuel fitting Use a liquid pipe thread sealant when installing fittings 1 Install in reverse order of removal 2 Tighten fuel line fitting to 16 20 Ib ft 3 Start the vehicle and leak check the propane fuel System at each serviced fitting 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 109 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM LOW PRESSURE LOCK OFF LPL REPLACEMENT UNDERHOOD Removal Procedure 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief Disconnect the negative battery cable Remove the air intake duct Loosen the hose clamp at the MAF sensor Dey Remove the engine air cleaner MAF sensor assembly Disconnect t
43. 999 2000 GM Medium Duty Chassis Service Manual Supplement Page 70 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM e A heated oxygen sensor wire A sensor pigtail Test Description may be mis routed and contacting the exhaust manifold The numbers below refer to the step numbers on the e An intermittent ground in the wire between the diagnostic table connector and the sensor e A poor ECU to the engine block ground 2 This step will determine if the fault is e f the above check out okay the problem may be currently present a faulty heated sensor 3 This step will determine if the HO2S is shorted and the cause of the fault Never solder the HO2S wires For proper wire and 4 This step will determine if the AF ECU is connector repair refer to Wiring Repairs in Engine the cause of the fault Electrical in the appropriate GM MD Service Manual 5 This test determines if the sensor wiring is the cause of the DTC 44 DTC 44 HO2S Circuit Low Voltage Bank 1 Sensor 1 Was the Alternative Fuels AF Powertrain On Board Diagnostic OBD System Check performed Go to AF Powertrain BD Go to Step 2 o 2e id Install a scan tool Idle the engine at normal operating temperature Operate the engine above 1200 RPM for two minutes 300 mV to Observe the H02S sensor reading on the scan 600 mV tool Does the scan tool indicate the bank 1 HO2S 1 voltage varying outside the specified range Go to Step 8 Go to Step 3 1 Disconnect the HO2S Bank 1
44. C to be set by the PCM or AF ECU 3 Observe the pressure reading on the secondary test port Go to AF Fuel Control System Is the fuel pressure within the specified value Diagnosis Go to Step 7 Inspect the air intake stream between the mixer assembly and the throttle body for leaks Inspect the vacuum hoses in the mixer area for proper connection and condition Inspect the fuel hose connection between the LPR and mixer assembly for damage or leakage Was a problem found and corrected GOTO S1ep 30 Gotorsten ce 1 Connect a water column gauge or a manometer to the secondary test port of the low pressure regulator LPR 2 Crank the engine and observe the pressure reading for the LPR secondary pressure Does the fuel pressure indicate a vacuum is present Go to Step 12 Go to Step 9 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 19 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM E o T wewis ve Ne 1 Remove the bonnet from the mixer assembly 2 Observe the air valve for movement while the engine is cranking Note Movement of the air valve will be minimal at cranking speeds Does the air valve move when the engine is cranked Go to Step 11 Go to Step 10 1 Inspect the air intake stream between the mixer assembly and the throttle body for vacuum leaks 2 Inspect the vacuum hoses in the mixer area for proper connection and condition Was a problem found and repaired Go to Step 30 Go to
45. C002 RED C001 BLU Alternative Fuel 1 Engine Control Unit AF ECU 1 FCS duty cycle means the ECU is issuing a lean command to control a rich condition A low FCS duty cycle means the ECU is issuing a rich command to control a lean condition At idle and low speeds the ECU will use the idle control solenoid ICS to maintain closed loop operation The ICS supplies fuel from the LPR secondary chamber below the mixer directly into the air stream For 1999 vehicles the ECU will command a 50 duty cycle to the ICS until airflow reaches approximately 25 g s For 2000 vehicles the ECU will command a 2596 7596 duty cycle to the ICS until airflow reaches approximately 100 g s The regulator control calve RCV is a normally closed vent valve located on top of the LPR During idle and normal driving conditions the RCV is closed This allows the FCS to control the pressure on top of the LPR secondary diaphragm During sudden throttle changes the RCV opens to vent the vacuum on top of the secondary diaphragm of the LPR which allows faster LPR output pressure response 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 23 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM The ETC solenoid accommodates a reduced power mode command from the PCM This is accomplished by venting the vacuum on top of the air valve diaphragm to atmosphere With atmospheric pressure the air valve will be lowered to the idle position in the
46. ECT sensor and the PCM Was a problem found Check the ECT sensor signal circuit for an open between the ECT sensor and the PCM Was a problem found Replace the ECT sensor Is the replacement complete Replace the PCM Go to Step 16 Go to Step 16 u Go to Step 17 Go to Step 2 Go to the applicable DTC Table System OK Important If the PCM is faulty reprogram the PCM Refer to PCM Replacement Programming The 7 4L LPG fuel system requires a unique PCM software calibration Is the replacement complete Operate the vehicle within the conditions for setting this DTC as specified in the supporting text Check to see if the MIL light still illuminates Did the diagnostic run and pass Are any ECU or PCM DTCs displayed that have not been diagnosed Repair the circuit as necessary Is the repair complete Go to Step 16 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 36 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 16 ECT Excessive Time to Closed Loop I ECT i 1 Sensor i Signal Engine Control Unit AF ECU EE Powertrain Control Module PCM i ECT Sensor 1 Signal Instrument Cluster A17 135 ECT IP Cluster Sensor Signal Engine Coolant Temperature ECT ECT Sensor Sensor Ground Powertrain Sensor Control Module PCM Circuit Description While the engine is warming the ECU monitors the ECT sensor in order to deter
47. ERAN RR RE gates ds 1 Amp LIQUID PETROLEUM GAS Commercial Propane Butane Boiling point F 30 Hg sse 944 9 lite edet eR 32 Specific gravity of air 60 F 30 Hg ssseee He MOO cm t Erat 2 00 Specific gravity of water 60 F 30 Hg sse Oai EE reete tere 0 58 Weight per gallon 60 F rrara aae AEE AEE AER REN E REE 4 85 BTU per gallon vaporized seeeeeH He 91 500 innen 102 600 BTU per pound vaporized uias a a r a 21 5605 c a 21 180 Air Fuel Ratio By Voluttie io eee eite deeds 238 10 1 2 eee 30 to 1 Best Power By Weight eco er eas VAS tol 35i t 14 3 to 1 Vapor Pressure Lbs Sq In Propane Butane zu ZU MEC O Act tt tedio Er eb a due QOH cess ote et as it je CE a bM scott 92 Fiti eai dodo sie aa dta OO ias erdoia i e E 1004 iio 124 GOF o ii ea die ee eae dls 1903 22 51 TOO Pins ec ecd tet eel uh etse bett ede 1908 Lenses 371 1203E 2 2E DIMBIBIUAP INIM 2404 stet 55 Propane Butane Octane number RON only ssssssssseeeee emen nennen 125 acte es 91 Octane number as it relates to gasoline approx eene 98 circ AE EE E Critical compression ratios ccc ceeceeeeee ee eeee cece ee eeeeee aa eeeeeeaaeeeeeeaaeeeeeeaaeeeeeaa 12 1 2 nnd 6 4 1 Best compression ratio range ssssseseeee 9 5 110 5 veered ate eee athe Propane Gasoline Weight pe
48. PL WHT 25 to 75 Red clip to 12V power Black clip to ground DVOM Set for duty cycle percentage and connect between pin A YEL and a good ground 4 With the engine idling observe the duty cycle reading of the FCS Is the FCS duty cycle within the specified range Go to Step 6 Go to Step 5 5 25 ES Is the FCS duty cycle below the specified value Goto Step 8 Goto Step 10 KA Will the engine rev to 2500 RPM EE Goto Step 7 Goto Step 13 1 Observe the scan tool MAF reading 2 Raise the engine speed to approximately 2500 RPM or greater than 28 g s MAF 3 Observe the duty cycle reading of the FCS 25 to 75 Is the FCS duty cycle within the specified range Go to Step 34 Goto Step 14 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 25 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM O PROPANE FUEL SYSTEM Aon Values Sep Am ves Ye 1 Connect a duty cycle monitoring tool at C012 test connector as follows FSA Yellow clip to pin A ORG Green clip to pin B PPL Red clip to 12V power Black clip to ground DVOM Set for duty cycle percentage and connect between pin A ORG and a good ground 2 Observe the duty cycle of the ICS Is the ICS duty cycle within the specified range 1 Using a DVOM backprobe the ICS electrical connector terminals 2 Observe the duty cycle of the ICS Is the ICS duty cycle within the specified range Remove t
49. S sensor or the circuit is shorted to low by checking for an extended lean condition This DTC is a type B DTC Conditions for Setting the DTC e The ECT is greater than 70 C 160 F e The oxygen sensor has been warm for at least 120 seconds The oxygen sensor is determined to be warm by the ECU if ECT is greater than 40 C 104 F and the mass air flow is above 11 g s for at least 120s e The ECU is in closed loop operation Powertrain i bios ood Alternative Fuel Control I Engine Control B2 1 Module PCM Seed ow Unit AF ECU I T a rr C001 BLU Heated Oxygen Sensor HO2S 1 Bank 2 e The HO2S Bank 2 Sensor 1 voltage is less than 0 02 volt 20 mV Action Taken When the DTC Sets The MIL will be turned on after 2 consecutive trips with test failures The system will operate in Open Loop if any DTC of the second HO2S Bank 1 Sensor 1 is set DTC 42 44 or 45 Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F from the start up coolant temperature and the engine coolant temperature exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 84 Website 5 29 03 Diagnosti
50. SYSTEM Ignition System Checks Note LPG being a gaseous fuel requires higher secondary ignition system voltages for the equivalent gasoline operating conditions e Check for the proper ignition voltage output with J 26792 or the equivalent Check the spark plugs for the following conditions Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Check for bare or shorted ignition wires Check for moisture in the distributor cap if applicable Check for loose ignition coil connections Important 1 If the engine starts but then immediately stalls remove the CKP sensor 2 Check for improper resistance or faulty connections 3 Check the Crankshaft Position CKP sensor resistance and connections Refer to Enhanced Ignition System in the GM MD Service Manual Engine Mechanical Checks Important The AF system works on a fumigation principle of fuel introduction and is more sensitive to intake manifold leakage than the gasoline fuel supply system e Check for the following Vacuum leaks Improper valve timing Low compression Bent pushrods Worn rocker arms Broken or weak valve springs Worn camshaft lobes Ref e Check the intake and exhaust manifolds for casting flash Exhaust System Checks e Check the exhaust system for a possible restriction Inspect the exhaust system for damaged or collapsed pipes nspect the muffler for signs of heat distress or for possible internal failure e Check for possible plug
51. Step 15 Go to Step 15 Are any additional DTCs set Repair the circuit as necessary Is the repair complete Repair the short to the ground in the IAT signal circuit Is the repair complete Replace the PCM Important If the PCM is faulty reprogram the PCM Refer to PCM Replacement Programming The 7 4L LPG fuel system requires a unique PCM software calibration Is the replacement complete Go to Step 15 Go to Step 16 Go to Step 2 Go to the applicable DTC Table System OK Operate the vehicle within the conditions for setting this DTC as specified in the supporting text Check to see if the MIL light still illuminates Did the diagnostic run and pass Are any ECU or PCM DTCs displayed that have not been diagnosed Replace the IAT Sensor Is the replacement complete Go to Step 15 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 43 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 25 IAT Sensor Circuit High Voltage Alternative Fuel as Engine Control ensor m Signal 1 Unit AF ECU eee ae 19 C001 BLU i Powertrain 1 uin Control Signal Module PCM I C2 BLU Sensor Intake Air Signal Temperature IAT Sensor IAT Sensor C1 RED p X4 a i IAT Powertrain M Control i Module PCM I Circuit Description The Intake Air Temperature IAT sensor is a thermo resistor located in the fresh air duct to the throttle
52. UEL SYSTEM IDLE CONTROL SOLENOID ICS REPLACEMENT Removal Procedure 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief Disconnect the negative battery cable Disconnect the ICS electrical connector Disconnect the ICS fuel hose from the LPR Remove the two 2 ICS solenoid mounting bolts and the solenoid Disconnect the fuel line from the ICS Oo RON 9 Installation Procedure 1 Install in reverse order of removal REGULATOR CONTROL VALVE RCV REPLACEMENT Removal Procedure 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief 2 Disconnect the negative battery cable 3 Disconnect the vacuum hose from the regulator control valve RCV 4 Unscrew the RCV from the LPR Installation Procedure Important e Do not use Teflon tape on any fuel fitting Use a liquid pipe thread sealant when installing fittings 1 Apply liquid pipe thread sealant to the RCV threads 2 Install in reverse order of removal FUEL MIXER REPLACEMENT Removal Procedure 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief 2 Disconnect the negative battery cable 3 Remove the fuel mixer plate Refer to Fuel Mixer Plate Replacement 4 Disconnect the three 3 vacuum hoses from the mixer Remove the ETC solenoid mounting bolt replacement Remove the six 6 mixer mounting screws Remove the mixer Remove th
53. al Supplement Page 102 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Rough Unstable or Incorrect Idle Stalling DEFINITION The engine runs unevenly at idle If severe enough the engine or vehicle may shake The engine idle speed may vary in RPM Either condition may be severe enough to stall the engine Preliminary Check e Refer to Important Preliminary Checks Sensor Checks e Check for silicon contamination from fuel or improperly used sealant The sensor will have a white powdery coating The sensor will result in a high but false signal voltage rich exhaust indication The Control Module will reduce the amount of fuel delivered to the engine causing a severe driveability problem e Check the Heated Oxygen Sensor HO2S performance Refer to DTC 44 HO2S Circuit Low Voltage Bank 1 Sensor 1 Refer to DTC 45 HO2S Circuit High Voltage Bank 1 Sensor 1 Refer to DTC 42 HO2S Insufficient Activity Bank 1 Sensor 1 Refer to DTC 64 HO2S Circuit Low Voltage Bank 2 Sensor 1 Refer to DTC 65 HO2S Circuit High Voltage Bank 2 Sensor 1 Refer to DTC 63 HO2S Insufficient Activity Bank 2 Sensor 1 Check the Engine Coolant Temperature ECT sensor using the scan tool to compare the engine coolant temperature with the ambient air temperature on a cold engine If the coolant temperature reading is more than 5 greater than or less than the ambient air temperature on a cold engine check for a high resistance in the coolant sensor circuit or the senso
54. an the specified value Go to Step 4 Go to Step 10 1 Turn OFF the ignition 2 Disconnect ECU connector C001 3 Turn ON the ignition Does the scan tool display a MAP sensor voltage less than the specified value Go to Step 8 Go to Step 5 Turn OFF the ignition Disconnect the MAP sensor connector Check for continuity of the MAP sensor signal circuit between the MAP and ECU connector Is there continuity Go to Step 6 Go to Step 16 Inspect the ECU connector for loose corroded or damaged pins Was a problem found Go to Step 16 Go to Step 7 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 51 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Replace the ECU Refer to ECU Replacement Is the action complete Turn OFF the ignition Disconnect the MAP sensor electrical connector Connect a jumper wire between the MAP sensor 5 volt reference circuit and the MAP sensor signal circuit Turn ON the ignition leaving the engine OFF Does the scan tool display a MAP sensor voltage near the specified value Turn OFF the ignition Remove the jumper wire Probe terminal B of the MAP sensor harness with a test lamp to B Turn ON the ignition Does the scan tool display a MAP sensor voltage near the specified value The DTC is intermittent If no additional DTCs are stored refer to Diagnosis Aids If additional DTCs are stored refer to those tables Are any additional DTCs set Check fo
55. at can cause an electrical system interference Normally the problem will occur when the faulty component is operating The improper installation of electrical devices such as lights 2 way radios electric motors etc The ignition secondary voltage shorted to a ground The Malfunction Indicator Lamp MIL circuit or the Diagnostic Test Terminal intermittently shorted to ground The Control Module grounds Loss of DTC Memory n order to check for the loss of the DTC Memory disconnect the Throttle Position TP sensor Idle the engine until the Malfunction Indicator Lamp illuminates The PCM and should store a Throttle Position DTC The Throttle Position DTC should remain in the memory when turning off the ignition DE Throttle Position DTC does not store and remain the Control Module is aulty The ECU memory may be checked in the same manner by selecting a DTC and intentionally setting the fault Additional Checks Check for an open diode across the A C compressor clutch and for other open diodes 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 93 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Hard Start Gus Ae DEFINITION The engine cranks OK but does not start for a long time The engine does eventually run or may start but immediately dies Preliminary Checks Refer to Hos pd dd M Preliminary Checks Make sure the vehicle s operator is using the correct starting Hos pd dd M Sensor
56. c Aids Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure IMPCO PROPANE FUEL SYSTEM Test Description The numbers below refer to the step numbers on the diagnostic table Check the following conditions 11 This step will determine if the fault is currently present e A heated oxygen sensor wire A sensor pigtail 12 This step will determine if the HO2S is may be mis routed and contacting the exhaust shorted and the cause of the fault manifold 13 This step will determine if the AF ECU is e An intermittent ground in the wire between the the cause of the fault connector and the sensor 14 This test determines if the sensor wiring is e A poor ECU to the engine block ground the cause of the DTC 64 e fthe above check out okay the problem is a faulty heated sensor Never solder the HO2S wires For proper wire and connector repair refer to Wiring Repairs in Engine Electrical DTC 64 HO2S Circuit Low Voltage Bank 2 Sensor 1 Value s Yes Was the Alternative Fuels AF Powertrain On Board Go to AF Diagnostic OBD System Check performed Powertrain OBD System Go to Step 2 check Install a scan tool Idle the engine at normal operating temperature Operate the engine above 1200 RPM for two 300 mV to minutes 600 mV Observe the H02S sensor reading on the scan tool Does the scan tool indicate the bank 2 HO2S 1 voltage varying outside the specified range Go to Step 8 Go to Ste
57. ctor Crank the engine The test light should illuminate Does the test light illuminate Go to Step 24 Go to Step 25 1 Disconnect the underbody LPL connector 2 Install a test light between the pins of the LPL connector 3 Turn the ignition ON The test light should illuminate for 2 seconds Does the test light illuminate Go to Step 18 Go to Step 23 Using a DVOM check the resistance of the underbody LPL 6 2 2 100 Is the resistance within the specified range Go to Step 19 Go to Step 27 1 Turn the ignition OFF Go to Step 21 Go to Step 20 2 Close the manual shut off valve on the LPG tank CAUTION When disconnecting LPG fuel lines liquid LPG may be present Perform this step in a well ventilated area 3 Loosen the fuel inlet hose fitting at the inlet of the underhood LPL Was fuel present when the fitting was loosened Remove the underbody LPL and filter assembly Remove the filter from the LPL assembly Empty the contents of the inlet side of the fuel filler onto a clean surface Inspect the contents of the fuel filter for an excessive amount of foreign material or water If necessary locate and repair the source of contamination Is the action complete Replace the fuel filter Refer to Fuel Filter Replacement The fuel supply system or hoses are plugged or restricted locate and repair the problem Is the action complete Go to Step 30 Go to Step 30 1999 2000 GM Medium Duty Chass
58. diagnostic procedure Clearing the DTCs will also clear valuable Freeze Frame and Failure Records data Inspect all related wiring and connections including the connections at the PCM These may cause an intermittent malfunction Check any circuitry that is suspected of causing an intermittent condition for the following conditions e Backed out terminals Improper mating Broken locks Improperly formed or damaged terminals Poor terminal to wiring connections Physical damage to the wiring harness Corrosion Test Description The numbers below refer to the step numbers on the diagnostic table 1 This step isolates if the customer complaint is a MIL or a driveability problem with no MIL 2 When the ignition switch is turned ON the scan tool should display serial data This step determines if the PCM is powered up 3 Refer to DTC Identification for a list of valid DTCs A faulty scan tool PCM Programming or PCM may result in an invalid DTC 4 This step enables the AF ECU DTC display mode 5 DTCs are displayed in ascending order Each DTC is flashed three 3 times prior to displaying the next available DTC When all stored DTCs have been displayed the AF ECU will begin the cycle again at DTC 12 until the AF ECU is returned to normal operation 6 This step will clear all AF ECU DTCs and reset the fuel trim to its initial value 7 This step verifies that the engine will start 8 Comparison of an actual control syst
59. dstescbeter 93 H rd St art 1 5 iine tre onse tetas cba AEAEE PANEN Aea A KAANE a 94 Cuts Outs MISSES NE EE 96 Hesitation Sag Stumble 2 cceeeece cece ee ee cece ee eeee cece eeeee ee eeee seca aeseeeeeeeaeseeeeeseeeenees 97 B ckfite intret EE A E 98 Lack of Power Sluggishness or Sponginess eere 99 Poor Fuel ECONOMY 5 cc2 lt c ccccccccccegezccecsasescccedetieeceesesiaccecetiachaceszccae stp ceasagiaccedstsccees 101 Rough Unstable or Incorrect Idle Stalling 2 ccceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeees 103 Surges Chuggles 1 1 2 1121 aana Anaa i Aaa aaa aaa 106 aisi sniman 108 Propane Fuel System Pressure Relief ccceessecceeeeeeeeeeeeeeeeeeeeeeeeeeenseeeeeeeseeeseees 108 Propane Fuel System Leak Test eeseeeeeeeeseeee eene nnne nnn 108 Propane Fuel Filter Replacement eseeeeeeeeeee nene 108 Low Pressure Lock off LPL Replacement Underbody 108 Low Pressure Regulator LPR Replacement eere 108 Low Pressure Lock off LPL Replacement Underhood 110 Fuel Mixer Cover Replacement ccccceeseeeeeeeeeeeeeneeeeeeeeeeseeeeeeeseeeeeeeseeeeeeneeeneeees 110 Electronic Throttle Control ETC Solenoid Replacement 111 Fuel Contr
60. e 1 Install in reverse order of removal 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 110 Website 5 29 03 Electronic Throttle Control ETC Solenoid Fuel Control Solenoid FCS IMPCO PROPANE FUEL SYSTEM Idle Control Solenoid ICS Fuel Mixer Outlet Elbow ELECTRONIC THROTTLE CONTROL ETC SOLENOID REPLACEMENT Removal Procedure 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief Disconnect the negative battery cable Remove the fuel mixer cover Refer to Fuel Mixer Cover Replacement Disconnect the ETC solenoid electrical connector Disconnect the two 2 vacuum hoses from the ETC solenoid Remove the ETC solenoid mounting bolt and the solenoid Installation Procedure 1 Install in reverse order of removal FUEL CONTROL SOLENOID FCS REPLACEMENT Removal Procedure 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief Disconnect the negative battery cable Remove the fuel mixer cover Refer to Fuel Mixer Cover Replacement Disconnect the FCS solenoid electrical connector Disconnect the two 2 vacuum hoses from the FCS solenoid Remove the FCS solenoid mounting bolt and the solenoid Installation Procedure 1 Install in reverse order of removal 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 111 Website 5 29 03 IMPCO PROPANE F
61. e connection at the PCM Go to Step 17 Goto Step 18 Go to Step 19 connector Was a problem found Repair the circuit as necessary Is the action complete Replace the PCM Important If the PCM is faulty reprogram the PCM Refer to PCM Heplacement Programming The 7 4L LPG fuel system requires a unique PCM software calibration i Is the action complete Go to Step 19 1 Bring the engine up to normal operating temperature 2 Run the engine above the specified value for at least 4 minutes 3 Turn OFF the engine and the ignition for at least 1500 RPM 10 seconds 4 Run the engine above the specified value for at least 4 minutes second time Did the MIL illuminate COLOSERE Salen Ok 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 69 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 44 HO2S Circuit Low Voltage Bank 1 Sensor 1 PPLANHT TANANHT S015 TANANHT Iion Power Ground Hozs Bark 42 Senso 81 Circuit Description The ECU supplies a voltage of about 0 45 volt between the HO2S high and HO2S low circuits The Heated Oxygen Sensor HO2S Bank 1 Sensor 1 varies the voltage within the range of about 1 0 1000 mV volt if the exhaust is rich down to about 0 1 100 mV volt if the exhaust is lean The sensor is like an open circuit and produces no voltage when it is below 360 C 600 F DTC 44 determines if the HO2S sensor or the circuit is shorted to low by checking for an
62. e mixer O ring Remove the four 4 outer baseplate to bracket mounting bolts e OND 10 Loosen the four 4 baseplate to elbow screws approximately v2 Installation Procedure 1 Install the mixer and the six 6 mounting screws 2 Install the O ring over the mixer and position between the outlet elbow and the baseplate 3 Tighten the four 4 baseplate to elbow screws 4 Install the four 4 outer baseplate to bracket mounting bolts 5 Install the ETC solenoid bolts 6 Connect the three 3 vacuum hoses to the mixer 7 Install the fuel mixer cover Refer to Fuel Mixer Cover 8 Connect the negative battery cable FUEL MIXER OUTLET ELBOW REPLACEMENT Removal Procedure 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief 2 Disconnect the negative battery cable 3 Remove the fuel mixer plate Refer to Fuel Mixer Plate Replacement 4 Remove the fuel mixer Refer to Fuel Mixer Replacement 5 Remove the idle control solenoid ICS Refer to Idle Control Solenoid ICS Replacement 6 Loosen the fuel vapor hose clamp at the elbow inlet fitting 7 Loosen the throttle body hose clamp at the elbow 8 Remove the fuel mixer elbow Installation Procedure Important e Do not use Teflon tape on any fuel fitting Use a liquid pipe thread sealant when installing fittings 1 Install in reverse order of removal 2 Start the vehicle and check the propane fuel Sys
63. ecutive trips with test failures The system will operate in Open Loop if any DTC of the second HO2S Bank 1 Sensor 1 is set DTC 42 44 or 45 Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F from the start up coolant temperature and the engine coolant temperature 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 79 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used Diagnostic Aids Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure A poor connection rubbed through wire insulation or a wire broken inside the insulation may cause an intermittent Check the following conditions e A poor connection or a damaged harness Check for the following conditions Backed out terminals Improperly formed or damaged terminals Poor terminal to wire connection Damaged harness e A poor ECU to the engine block ground e Faulty Fuel Control Solenoid FCS e Faulty Regulator Control Valve RCV e Faulty Low Pressure Regulator e Exhaust leaks If there is an exhaust leak the engine may pull the outside air into the exhaust and past the sensor e Vacuum or crankcase
64. ed and position of throttle valve opening The air valve assembly measures the air flow into the engine by moving precisely in response to the demands of the engine and throttle valve position The controlled pressure drop of 0 2 to 0 5 psi 6 to 13 8 water column set up by the metering spring provides the signal or force necessary to draw fuel into the air stream within the carburetor The gas metering valve is attached to the air valve assembly and is shaped to admit the correct amount of fuel from the gas jet to mix with incoming air at any opening of the air valve ALTERNATIVE FUEL ENGINE CONTROL UNIT AF ECU The alternative fuel engine control unit AF ECU controls the propane fuel system The AF ECU monitors various engine and vehicle functions to provide the correct amount of fuel under all operating conditions This provides excellent driveability and fuel economy while maintaining reduced exhaust emission levels LOW PRESSURE LOCK OFF LPL The electric low pressure lock off solenoids provide electronic fuel shut off for pressures up to 312 psi It is a closed solenoid operated lock off with a 1 4 diameter fuel orifice If the lock off fails it is designed to fail in the closed position The solenoid has a high temperature coil and is both UL and CGA approved CONTROL SOLENOIDS FUEL CONTROL SOLENOID FCS An electrically actuated control solenoid used to trim fuel mixtures by controlling the pressure on top of t
65. em data with the Typical Scan Tool Data Values is a quick check to determine if any parameter is not within limits A base engine problem i e advanced cam timing may substantially alter sensor values 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 12 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Alternative Fuel AF Powertrain OBD System Check Sep Action ves ve Go to Malfunction Indicator Lamp Circuit Check in the GM MD Service Manual Go to Step 2 Important Check for applicable service bulletins before proceeding with this test Perform this test only if there is a driveability complaint or if you have been sent to this table from another section in the service information Important Do not clear DTCs unless instructed by this diagnostic 1 Turn off the ignition 2 Connect the scan tool 3 Turn ON the ignition leaving the engine OFF 4 Observe the MIL Does the MIL illuminate for 2 seconds then turn off Observe the DTC information If the DTC status Last Test Failed Test Failed Test Failed This Ignition MIL Request or History DTC are set save the DTC Freeze Frame and the Failure Records information as necessary using the scan tool Go to the Applicable DTC Table in the GM MD Service Manual Go to Step 4 Go to Step 5 Go to Go to Step 6 Driveability Symptoms Were any of these DTCs set Turn the ignition switch from OFF to RUN 3 times within 10 seconds D
66. em found 1 Turn ON the ignition 2 Compare the ECT display on the scan tool to the actual coolant temperature The values should be close Are they close Start the engine Idle at normal operating temperature Operate the vehicle within the conditions for setting this DTC as outlined in the supporting text Check to see if the MIL light still illuminates Did the diagnostic run and pass Go to Step 11 Go to Step 2 Go to the applicable DTC Table System OK Are any ECU or PCM DTOs displayed that have not been diagnosed Replace the ECT sensor Is the replacement complete Go to Step 10 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 39 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM BLANK 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 40 Website 5 29 03 DTC 23 IAT Sensor Circuit Low Voltage Alternative Fuel uM Engine Control ensor T Signal 1 Unit AF ECU ewe ee ee ee ee ee eet N C001 BLU IMPCO PROPANE FUEL SYSTEM i Powertrain k a Control Signal Module PCM E C2 BLU IAT Sensor Intake Air Signal Temperature IAT Sensor IAT Sensor RED r Y i IAT Powertrain sid Control Module PCM j Circuit Description The Intake Air Temperature IAT sensor is a thermo resistor located in the fresh air duct to the throttle body to monitor the temperature of the air entering the throttle
67. en in the 5 volt reference circuit or the sensor ground circuit results in a DTC 14 3 If the fault is present the engine coolant temperature voltage measures greater than Use the Temperature vs Resistance Value Table to 4 395 volts test the coolant sensor at various temperature levels 5 This test will determine if the ECU is the in order to evaluate the possibility of a skewed mis cause of DTC 14 scaled sensor A skewed sensor could result in DTC 14 ECT Sensor Circuit High Voltage Value s Yes mo Was the Alternative Fuels AF Powertrain On Board Go to AF Diagnostic OBD System Check performed Powertrain OBD System Go to Step 2 enak 1 Connect the scan tool Go to DTC 2 Start the engine P0118 3 ObDserve the ECT sensor reading 35 C 31 F ECT Sensor Circuit High Voltage in the GM MD Does the scan tool display the ECT sensor reading Service LESS than the specified value Manual Go to Step 3 Using a DVOM backprobe the ECT sensor signal in the ECU connector 4 39V Does the DVOM display the ECT sensor signal GREATER than the specified value Go to Step 4 Go to Step 5 1 Turn the engine OFF 2 Disconnect ECU connector C001 3 Turn the ignition ON 4 39V Does the DVOM display the ECT sensor signal GREATER than the specified value Go to Step 7 Go to Step 6 Disconnect the ECT sensor Using a DVOM check for continuity of the ECT circuit between the ECT connector and the ECU Is there continuity Go to Step
68. ep 5 1 Turn the engine OFF 2 Disconnect ECU connector C001 3 Turn the ignition ON 0 019 V Does the DVOM display the ECT sensor signal LESS than the specified value Go to Step 7 Go to Step 6 1 Disconnect the ECT sensor 2 Using a DVOM check for continuity of the ECT circuit between the ECT connector and the ECU Is there continuity Go to Step 9 Go to Step 13 Replace the ECU Refer to ECU Replacement Go to Step 16 Is the action complete Turn the ignition OFF Disconnect the ECT sensor connector Turn the ignition ON Observe the engine coolant temperature 35 C 31 F parameter on the scan tool Is the ECT sensor at the specified value Go to Step 10 Go to Step 8 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 35 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM tion Values Go to Step 11 Jumper the ECT sensor signal circuit to a known good ground 140 C 284 F Go to Step 12 Go to the applicable DTC Table Go to Step 13 Go to Step 14 Go to Step 13 Go to Step 15 Go to Step 13 Go to Step 15 Is the ECT sensor at the specified value The DTC is intermittent If no additional DTCs were stored refer to the Diagnostic Aids If any additional DTCs are stored refer to those tables Are any additional DTCs set Inspect the ECT sensor connector and the PCM connector for the proper connection Was a problem found Check the ECT sensor ground circuit for an open between the
69. erate the vehicle within the conditions for setting this DTC as specified in the supporting text Check to see if the MIL still illuminates Did the diagnostic run and pass Go to Step 15 Go to Step 2 Are any ECU or PCM DTOs displayed that have not been diagnosed Go to Applicable DTC Table System OK 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 61 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 41 CKP Sensor Circuit Performance t i CKP CKP 12V TACH 1 Sensor Sensor Ignition Output Signal Ground Feed Signal DK BLU WHT 026 WHT Crankshaft Position CKP Sensor 1 Powertrain Control i Module PCM i 1 1 i Alternative Fue Engine Control Unit AF ECU I TACH i Input 1 Signal i me mim ume mm d a i Ri B ms am fm a os a A C003 CLR 121 Circuit Description The Crankshaft Position CKP sensor sends a reference signal to the Engine Control Unit ECU in order to indicate the engine RPM Loss of this signal or intermittent operation of the CKP sensor will set DTC 41 This may trigger an ECU DTC before a PCM DTC as the AF ECU is slightly more sensitive to a marginal CKP sensor This DTC is a type A DTC Conditions for Setting the DTC e None of the following DTCs are active 36 37 e MAF is detecting greater than 3 g s and no RPM signal has been received Action Taken When the DTC Sets If a CKP input fault is detected the ECU will set DTC
70. es Check the Control Module grounds for being clean tight and in their proper location Check the vacuum hoses for splits kinks and proper connections as shown on the Vehicle Emission Control Information Label Check thoroughly for any type of leak or restriction Check for air leaks at all the mounting areas of the intake manifold sealing surfaces Check for proper installation of the mixer module assembly Check for air leaks at the mixer assembly Check the ignition wires for the following conditions Cracking Hardness Proper routing Carbon tracking Check the wiring for the following items Proper connections Pinches Cuts The following symptom tables contain groups of possible causes for each symptom and cover several engines The following symptom tables cover several engines The order of these procedures is not important If the scan tool readings do not indicate the problems then proceed in a logical order easiest to check or most likely to cause first In order to determine if a specific vehicle is using a particular system or component refer to the Control Module Wiring Diagrams in the GM MD Service Manual for an application Symptom Verify the customer complaint Locate the correct symptom table Check the items indicated under that symptom 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 92 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Intermittents DEFINITION T
71. extended lean condition This DTC is a type B DTC Conditions for Setting the DTC e The engine is running at greater than 500 RPM e The ECT is greater than 70 C 160 F e The oxygen sensor has been warm for at least 120 seconds The oxygen sensor is determined to be warm by the ECU if ECT is greater than 40 C 104 F and the mass air flow is above 17 g s for at least 120s e The ECU is in closed loop operation e The HO2S Bank 1 Sensor 1 voltage is less than 0 02 volt 20 mV Allernative Fue Engine Control Unit AF ECU C2 BLU 4 P Co01 BLU 1653 C006 PPLIWHT TANANHT Heated Oxygen Sensor H025 1 Bank 1 Action Taken When the DTC Sets The MIL will be turned on after 2 consecutive trips with test failures The system will operate in Open Loop if any DTC of the second HO2S Bank 2 Sensor 1 is set DTC 63 64 or 65 Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F from the start up coolant temperature and the engine coolant temperature exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used Diagnostic Aids Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure Check the following conditions 1
72. ged catalytic converter Refer to Restricted Exhaust System Diagnosis or Exhaust System in the GM MD Service Manual Additional Checks e Verify the correct PCM software is installed 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 95 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Cuts Out Misses DEFINITION A surging or jerking that follows engine speed usually more pronounced as the engine load increases which is not normally felt above 1500 RPM or 48 km h 30 mph The exhaust has a steady spitting sound at idle low speed or hard acceleration for the fuel starvation that can cause the engine to cut out Preliminary Checks e Refer to Important Preliminary Checks Ignition System Checks Start the engine Wet down the secondary ignition system with water from a spray bottle and look listen for arcing or misfiring as you apply water Check for proper ignition output voltage with spark tester J 26792 Check for a cylinder misfire Remove the spark plugs in these cylinders and check for the following conditions e Insulation cracks Wear Improper gap Burned electrodes Heavy deposits Visually Physically inspect the secondary ignition for the following Ignition wires for arcing cross firing and proper routing Ignition coils for cracks or carbon tracking Engine Mechanical Checks Perform a cylinder compression check Check the engine for the following Improper valve timing Bent pushrods Worn rocker arms Worn
73. he LPL electrical connector Disconnect the LPG fuel line from the LPR inlet fitting 9 Disconnect the ICS fuel line from the LPR 10 Remove the two 2 LPR to LPR bracket bolts 11 Remove the three 3 LPR bracket to crossover bracket bolts 12 Remove the one 1 LPR support bracket bolt from the intake manifold 13 Remove the two 2 LPL mounting bolts 14 Unscrew the LPL from the LPR oo N Disconnect the MAF sensor electrical connector Installation Procedure Important e Do not use Teflon tape on any fuel fitting Use a liquid pipe thread sealant when installing fittings Apply pipe thread sealant to the LPR inlet fitting 2 Install the LPL to the LPR Tighten the LPL finger tight plus 1 to 2 turns and place the LPL in the correct position Install in reverse order of removal Tighten the fuel line fitting to 16 20 lb ft Start the vehicle and leak check the propane fuel System at each serviced fitting e RO FUEL MIXER COVER REPLACEMENT Removal Procedure 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief 2 Disconnect the negative battery cable 3 Disconnect the IAT sensor electrical connector 4 Disconnect the PCV breather hose from the fuel mixer cover 5 Loosen the hose clamp at the fuel mixer cover inlet 6 Remove the six 6 fuel mixer cover bolts and the cover 7 Remove the IAT grommet from the fuel mixer cover Installation Procedur
74. he base of the LPR with engine coolant A sponge located in the primary chamber absorbs any liquid fuel and prevents it from entering the secondary chamber In the second stage the vaporized fuel is drawn into the secondary chamber where the pressure is reduced to approximately negative 1 5 of water column 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 5 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM FUEL MIXER The IMPCO Model 425 fuel mixer is an air fuel metering device and is completely self contained It requires no linkage or idle vacuum line to the intake manifold The mixer is an air valve design utilizing a relatively constant pressure drop to draw fuel into the mixer from cranking to full load The vacuum applied to the air valve working against a spring located on top of the valve correctly positions the air valve to meter the proper amount of fuel for any given engine speed and load The pressure drop that is controlled by the air valve spring provides the force to draw fuel into the air stream The upward movement of the diaphragm controls the fuel flow in the venturi air valve A pressure drop under the air valve of approximately 0 2 psi 6 water column of pressure is required to lift the air valve off its seat Approximately 0 5 psi 13 8 water column lifts the valve to the top of its travel in full open position Lowered pressure communicated to the top of the diaphragm varies with engine spe
75. he hose from the RCV valve and install a vacuum cap over the RCV port Operate the engine at IDLE for approximately 10 15 seconds Observe the duty cycle reading of the FCS Is the FCS duty cycle within the specified range 1 Observe the scan tool MAF reading 2 Raise the engine speed to approximately 2500 RPM or greater than 28 g s MAF 11 3 Observe the duty cycle reading of the FCS Is the FCS duty cycle within the specified range 1 Turn the engine OFF 2 Disconnect the ECU connector C002 3 Disconnect the FCS electrical connector 4 Check the FCS ground circuit in terminal B YEL 12 for continuity to the ECU connector 5 Check the FCS ground circuit in terminal B YEL for short to ignition power or ground Was a problem found and repaired 48 to 52 1999 or 25 to 75 2000 48 to 52 1999 or 25 to 75 2000 25 to 75 25 to 75 Go to Step 9 Go to Step 26 Go to Step 15 Go to Step 16 Go to Step 36 Go to Step 16 Go to Step 16 Go to Step 11 Go to Step 12 Go to Step 24 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 26 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Sep 4Adon Ves Yes Ne 1 Turn the ignition OFF 2 Remove the mixer bonnet assembly 3 Start the engine Note This action may set AF ECU and PCM 12 6 V to diagnostic codes for the MAF sensor 15 1 V 4 Using a DVOM backprobe the ETC electrical connector ter
76. he problem may or may not turn ON the Malfunction Indicator Lamp MIL or store a Diagnostic Trouble Code DTC Preliminary Checks Refer to Important Preliminary Checks Do not use the DTC tables If a fault is an intermittent the use of the DTC tables may result in the replacement of good parts Faulty Electrical Connections or Faulty electrical connections or wiring can cause most intermittent problems Wiring Check the suspected circuit for the following conditions Connectors poorly mated Terminals not fully seated in the connector backed out Terminals not properly formed or damaged Terminal to wires poorly connected Terminal tension insufficient Carefully remove all the connector terminals in the problem circuit in order to ensure the proper contact tension If necessary replace all the connector terminals in the problem circuit in order to ensure the proper contact tension Checking for poor terminal to wire connections requires removing the terminal from the connector body in Road Test If visual and physical check does not locate the cause of the problem drive the vehicle with a J 39200 connected to a suspected circuit or use a scan tool When the problem occurs an abnormal voltage or scan reading indicates the problem may be in that circuit Intermittent Malfunction Indicator The following components can cause intermittent MIL and no DTC s Lamp MIL e A defective relay Control Module driven solenoid or a switch th
77. he regulators secondary diaphragm Controlled by the ECU the solenoid translates a duty cycle into a regulated vacuum signal The fuel control solenoid meters air valve vacuum to the regulator to lean fuel mixtures or references atmospheric pressure to richen fuel mixtures IDLE CONTROL SOLENOID ICS An electrically actuated control solenoid used to meter fuel to the engine during idle and low speed operation Controlled by the ECU the idle control solenoid will be shut off after certain engine speed and load conditions are met ELECTRONIC THROTTLE CONTROL ETC SOLENOID An electrically actuated control solenoid used to control the mixer air valve If the AF ECU detects a Throttle Actuator Control TAC fault the ETC solenoid vents the air valve vacuum to atmosphere causing the air valve to close and forcing an idle condition REGULATOR CONTROL VALVE RCV The regulator control valve RCV is mounted on the regulator cover The RCV is a one way check valve that opens at 10 12 of water column and permits quick response of the secondary diaphragm during wide open throttle operation 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 6 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DIAGNOSTIC INFORMATION AND PROCEDURES Specifications Temperature vs Resistance 28680 52700 100700 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 7 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM
78. iagnostic run and pass Aids Go to Step 7 Check for a short to ground or short to ignition power in the CKP signal circuit Check for a load on the CKP signal circuit malfunctioning tachometer Check for proper pin tension at the PCM connector Was a problem found and repaired Inspect the ECU connector and pins Was a problem found 4 Using a DVOM check for continuity of the CKP sensor signal circuit between the PCM and Was a problem found Go to Step 8 Go to Step 6 Go to DTC PO336 CKP Sensor Circuit Performance in the GM MD Service Go to Step 10 Manual Go to Step 8 Go to Step 9 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 63 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM ation Values ves m Repair the open or damaged circuit Go to Step 10 Go to Step 10 ws Is the action complete Replace the ECU Refer to ECU Replacement Is the action complete Clear the DTC Operate the vehicle within the conditions for setting this DTC as specified in the supporting text Check to see if the MIL still illuminates Did the diagnostic run and pass Go to Step 11 Go to Step 2 Are any ECU or PCM DTCs displayed that have not Go to the 11 been diagnosed applicable DTC System OK table 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 64 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 42 HO2S Insufficient Activity Bank 1 Sensor 1
79. ilation Valve for proper operation by placing a finger over the inlet hole in the valve end several times The valve should snap back If not replace the valve Refer to Crankcase Ventilation System in the GM MD Service Manual 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 104 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Engine Mechanical Check Check the engine for the following Broken motor mounts Improper valve timing Low compression Bent pushrods Worn rocker arms Broken or weak valve springs Worn camshaft lobes 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 105 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Surges Chuggles DEFINITION The engine has a power variation under a steady throttle or cruise The vehicle feels as if it speeds up and slows down with no change in the accelerator pedal Preliminary Checks Refer to Important Preliminary Checks Be sure the driver understands the Torque Converter Clutch operation Be sure the driver understands the A C Compressor operation Use the scan tool to make sure the reading of the Vehicle Speed Sensor VSS matches the vehicle speedometer This excludes vehicles with electronic transmissions where some variation between the VSS and the speedometer is normal Sensor Checks Check the Heated Oxygen Sensor HO2S performance Refer to DTC 44 HO2S Circuit Low Voltage Bank 1 Sensor 1 Refer to DTC 45 HO2S Circuit High Voltage Bank 1 Senso
80. ions e Check for the proper ignition coil output voltage using the spark tester J26792 or the equivalent Check the spark plug wires by connecting an ohmmeter to the ends of each wire in question If the meter reads over 30 000 ohms replace the wires Note The vehicle may be equipped with low resistance plug wires refer to MD service manual for proper plug wire resistance e Check for deteriorated spark plug wire insulation e Check the spark plugs Remove the plugs and inspect them for the following conditions Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Check the ignition system Refer to gnition System Diagnosis in the GM MD Service Manual Engine Mechanical Check Important The AF system works on a fumigation principle of fuel introduction and is more sensitive to intake manifold leakage than a gasoline fuel supply system e Check the engine for the following Improper valve timing Engine compression Manifold vacuum leaks Intake manifold gaskets Sticking or leaking valves Exhaust system leakage e Check the EGR operation for being open all the time Refer to EGR System Diagnosis in the GM MD Service Manual e Check the intake and exhaust system for casting flash or other restrictions Fuel System Checks e Perform a fuel system diagnosis Refer to AF Fuel System Diagnosis Additional Checks e Proper PCM software calibrations e Check the EGR gasket for a faulty or loose fit e
81. iption vehicle using the same sensor is a good way to check the accuracy of a suspect sensor Readings The numbers below refer to the step numbers on the should be the same 0 4 volt diagnostic table Refer to ntermittents Important The electrical connector must remain 3 This step determines if DTC 34 is the result securely fastened of a hard failure or an intermittent condition Important After removing the MAP sensor from the 4 With the ECU connector disconnected and intake manifold replace the MAP sensor to intake the voltage still present this eliminates the manifold seal ECU as the possible cause of the fault 8 By jumping the 5 volt reference to the signal circuit this step determines if the sensor is at fault or if there is a problem with the circuit wiring 9 The scan tool may not display 5 volts The important thing is that the PCM recognized the voltage as more than 4 volts indicating that the PCM and MAP signal are okay 34 MAP Sensor Circuit Low Voltage Sep tion O O O o No Was the Alternative Fuels AF Powertrain On Board Go to AF Diagnostic OBD System Check performed Powertrain OBD System heck Go to Step 2 Ghee 1 Connect the scan tool 2 Turn the ignition ON 0 10 V Does the scan tool display a MAP sensor voltage less than the specified value Go to Step 4 Go to Step 3 Using a DVOM backprobe the MAP sensor signal in the ECU connector Does the DVOM display the MAP sensor signal less th
82. is DTC is a type B DTC Conditions for Setting the DTC e None of the following DTCs are active 21 22 and 26 e MAP circuit voltage is less than 0 098 volts e TP sensor position is less than 4 at RPMs less than 1200 or TP sensor position is greater than 20 at RPMs greater than 1300 Powertrain Controt Alternative Fuel Engine Control 1 Unit AF ECU C001 BLU Module PCM Action Taken When the DTC Sets The ECU sets the DTC 34 after 2 consecutive driving cycles with the fault active Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F from the start up coolant temperature and the engine coolant temperature exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used Diagnostic Aids Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure With the ignition ON and the engine OFF the manifold pressure is equal to the atmospheric pressure with the signal voltage high The ECU uses this information as an indication of the altitude of the vehicle 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 50 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Comparison of this reading with a known good Test Descr
83. is Service Manual Supplement Page 21 Is the action complete Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Sep Action O ewe Yes Ne Turn OFF the ignition Connect the test light to chassis ground and probe pin A of the LPL connector Crank the engine The test light should illuminate Does the test light illuminate Go to Step 24 Go to Step 25 Go to Step 30 Go to Step 30 Go to Step 30 Repair the open in the lock off ground circuit Refer to Wiring Repairs in the GM MD Service Manual Is the action complete Repair the open in the lock off power circuit Refer to Wiring Repairs in the GM MD Service Manual Is the action complete Replace the low pressure regulator LPR Refer to Low Pressure Regulator Replacement Is the action complete Replace the mixer assembly Refer to Fuel Mixer Replacement Is the action complete The fuel supply system is operating normally if a failure of the fuel control solenoids is suspected Refer to AF Fuel Control System Diagnosis 1 Install the test plug in the LPR secondary chamber 2 If you were sent to this routine by another diagnostic chart return to the previous diagnostic procedure System OK System OK 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 22 Is the action complete Disconnect all test equipment Install the primary and secondary test port plugs Start the engine Using SNOOP 6 or equivalent leak
84. is open or has high resistance repair as necessary Is the action complete Replace the MAF sensor Go to Step 21 Go to Step 21 Is the action complete Replace the PCM Important If the PCM is faulty reprogram the PCM Refer to PCM Replacement Programming The 7 4L LPG fuel system requires a unique PCM software calibration Go to Step 21 Go to Step 22 Go to Step 2 Go to the applicable DTC Table System OK 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 57 Is the action complete Operate the vehicle within the conditions for setting this DTC as specified in the supporting text Check to see if the MIL light still illuminates Did the diagnostic run and pass Are any ECU or PCM DTCs displayed that have not been diagnosed Locate the open in the ignition feed circuit to the MAF sensor Repair the open in the ignition feed circuit to the MAF sensor Is the action complete Go to Step 21 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 37 MAF Sensor Circuit High Frequency Sagral IGN RLYVIM Circut Breaker YEL 492 ignition Power Circuit Description The Mass Air Flow MAF sensor measures the amount of air entering the engine during a given time The ECU uses the MAF information for fuel delivery calculations A large quantity of air entering the engine indicates an acceleration or high load situation A small quantity of air indicates deceleration or idle Thi
85. is will be accompanied by lean shorted and the cause of the fault driveability conditions and a powdery white 17 This step will determine if the AF ECU is deposit on the sensor the cause of the fault e Faulty HO2S Bank 2 Sensor 1 If the HO2S 18 This test determines if the sensor wiring is Bank 2 Sensor 1 is internally shorted the the cause of the DTC 65 HO2S Bank 2 Sensor 1 voltage displayed will DTC 65 HO2S Circuit High Voltage Bank 2 Sensor 1 Value s Yes mo Go to AF Powertrain OBD System Check Was the Alternative Fuels AF Powertrain On Board Diagnostic OBD System Check performed Go to Step 2 Install a scan tool Idle the engine at normal operating temperature Operate the engine above 1200 RPM for two 300 mV to minutes 600 mV Observe the H02S sensor reading on the scan tool Does the scan tool indicate the bank 2 HO2S 1 voltage varying outside the specified range Go to Step 8 Go to Step 3 1 Disconnect the HO2S Bank 2 Sensor 1 sensor electrical connector 350 mV to 2 Observe the H02S sensor reading on the scan 550 mV tool Does the scan tool indicate the bank 2 HO2S 1 voltage is within the specified range Goto Step 6 Go to Step 4 Turn the ignition OFF Disconnect ECU connector C001 Tur the ignition ON 350 mV to Observe the H02S sensor reading on the scan 550 mV tool Does the scan tool indicate the bank 2 HO2S 1 voltage within the specified range Go to Step 9 Go to Ste
86. isplay a IAT sensor reading above the specified value Go to Step 8 Go to Step 6 Using a DVOM backprobe the IAT sensor signal in the ECU connector 0 019 V Does the DVOM display the IAT sensor signal less ifi than the specified value Go to Step 5 Go to Step 10 Disconnect ECU connector C001 Go to Step 6 Go to Step 11 r o Disconnect the IAT sensor connector Check for continuity of the IAT sensor signal circuit between the connectors Is there continuity Replace the ECU Refer to ECU Replacement Inspect the ECU connector for loose corroded or damaged pins Was a problem found Goto Step 11 Goto Step 7 Go to Step 15 EN Is the action complete Turn OFF the engine Turn ON the ignition Disconnect the IAT sensor connector 39 C 38 F Observe the IAT sensor voltage on the scan tool Is the IAT sensor voltage at the specified value Go to Step 13 Go to Step 9 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 42 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Adin va Go to Step 12 Go to Step 14 Turn OFF the ignition Disconnect the PCM connector Using a DVOM check the IAT sensor signal circuit for a short to ground Was a problem found The DTC is intermittent If no additional DTCs are stored refer to the Diagnostic Aids If additional DTCs were stored refer to those tables Go to the Reter to applicable DTC Diagnostic Table Aids Go to
87. l display the IAT sensor at the 284 F specified value Go to Step 11 Goto Step 12 The DTC is intermittent If no additional DTCs are Go to the applicable DTC Table stored refer to the Diagnostic Aids If additional DTCs are set refer to those tables Go to Step 13 Go to Step 14 Go to Step 13 Go to Step 15 Are any additional DTCs set Inspect the sensor connector and the PCM connector for the proper connection Was a problem found Check the IAT sensor ground circuit for an open between the IAT sensor and the PCM Was a problem found Repair the circuit as necessary Go to Step 16 Go to Step 16 Go to Step 16 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 46 Is the repair complete Replace the IAT Sensor Is the replacement complete Replace the PCM Important If the PCM is faulty reprogram the PCM Refer to PCM Replacement Programming The 7 4L LPG fuel system requires a unique PCM software calibration Is the replacement complete Check the sensor signal circuit for an open between the IAT sensor PCM and the ECU Was a problem found Go to Step 13 Go to Step 15 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Sep Adon S Vau Yes Operate the vehicle within the conditions for setting this DTC as specified in the supporting text Check to see if the MIL light still illuminates Did the diagnostic run and pass Go to Step 17 Go to Step 2 Are any ECU
88. l in reverse order of removal Tighten fuel fittings finger tight plus 1 to 2 turns Tighten fuel line fittings to 16 20 lb ft Start the vehicle and leak check the propane fuel system and each serviced fitting AON 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 108 Website 5 29 03 Regulator Control Valve RCV Underhood Low Pressure Regulator LPR Bracket Crossover Bracket LOW PRESSURE REGULATOR LPR REPLACEMENT 1 Removal Procedure m Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief Disconnect the negative battery cable Drain the radiator Remove the air intake duct Loosen the hose clamp at the MAF sensor Disconnect the MAF sensor electrical connector Remove the engine air cleaner MAF sensor assembly 9 Disconnect the LPL electrical connector 10 Disconnect the LPG fuel line from the LPR inlet fitting 11 Disconnect the ICS fuel line from the LPR 12 Remove the two 2 LPR to LPR bracket bolts 13 Remove the three 3 LPR bracket to crossover bracket bolts 14 Remove the one 1 LPR support bracket bolt from the intake manifold 15 Remove the two 2 LPL mounting bolts 16 Disconnect the three 3 vacuum hoses from the top of the LPR 17 Disconnect the supply and return coolant lines from the LPR 18 Disconnect the fuel vapor hose from the LPR outlet fitting 19 Remove the LPR and LPL assembly
89. lant Temperature ECT sensor with the scan tool Compare the engine coolant temperature with the ambient air temperature on a cold engine If the coolant temperature reading is more than 5 degrees greater or less than the ambient air temperature on a cold engine check for high resistance in the coolant sensor circuit Refer to DTC P0118 ECT Sensor Circuit High Voltage or DTC P1115 ECT Sensor CKT Intermittent High Voltage in the GM MD Service Manual Check the Mass Air Flow MAF sensor Check the spark plugs Remove the plugs and inspect them for the following conditions Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Check the ignition wires for the following items Cracking Hardness Proper connections Check the engine coolant level Check the engine thermostat for always being open or for the wrong heat range Refer to Thermostat Diagnosis in Engine Cooling in the GM MD Service Manual 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 101 IMPCO PROPANE FUEL SYSTEM Additional Check Check the transmission shift pattern Refer to the Transmission Controls section in the GM MD Service Manual Check for Torque Converter Clutch TCC operation Refer to Torque Converter Clutch Solenoid in Automatic Transmission in the GM MD Service Manual Check for proper calibration of the speedometer Check for dragging brakes 1999 2000 GM Medium Duty Chassis Service Manu
90. minals 5 Observe the voltage reading at the ETC connector Is the voltage within the specified range Go to Step 28 Go to Step 18 Remove the hose from the RCV valve and install a vacuum cap over the RCV port Operate the engine at 2500 RPM for approximately 15 seconds With the engine running at 2500 RPM observe 25 to 75 the FCS duty cycle at the FSA or the DVOM Is the FCS duty cycle within the specified range Goto Step 15 Go to Step 32 Replace the regulator control valve RCV Refer to Regulator Control Valve Replacement Is the action complete Go to Step 36 1 Connect the positive lead of the DVOM to an ignition power source 48 to 52 2 Backprobe the ICS connector pin B ORG 1999 3 Connect the negative lead of the DVOM to Or terminal B 25 to 7596 in 2000 Is the ICS duty cycle within the specified range Goto Step 27 Goto Step 17 1 Disconnect the ECU connector C002 2 Check the ICS ground circuit between the ICS connector terminal B and C002 for an open or short to ignition power or ground Was a problem found and repaired Goto Step 36 Go to Step 21 1 Connect the negative lead of the DVOM to a known good ground 2 Backprobe the ETC solenoid connector pin A GRY 12 6 V to 3 Connect the positive lead of the DVOM to 15 1 V terminal A Is the ETC voltage within the specified range Go to Step 19 Go to Step 20 Check the ETC ground circuit and connections between the ETC solenoid connector ECU C00
91. mine how long the engine takes to achieve a specified coolant temperature increase required for a Closed Loop operation A DTC sets if the ECU determines that the engine does not achieve a predetermined engine temperature increase in a specified amount of time This DTC will not run if either the intake air or the engine coolant temperature measure below a specific temperature The ECU will only run this DTC on a cold start and only once per cold start This DTC is a type A DTC Conditions for Setting the DTC The following conditions will set the DTC e Engine run time is greater than 600 seconds e None of the following DTCs are active 14 15 23 25 e Intake air temperature is greater than 5 F 15 C e Vehicle speed is greater than 5 MPH e The ECT at start is less than 91 F 33 C e The ECT is greater than 1 F 17 C e ECT has not increased by 25 C Action Taken When the DTC Sets The ECU will set DTC 16 and illuminate the MIL light after 1 fault has occurred Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F from the start up coolant temperature and the engine coolant temperature exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used 1999 2000 GM Medium
92. n present A DTC has developed an open This DTC is a type B DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has Conditions for Setting the DTC risen 40 C 72 F from the start up coolant temperature and the engine coolant temperature e Engine speed is greater than 500 RPM exceeds 70 C 160 F during that same ignition e Engine run time is greater than 120 seconds cycle or the code clearing procedure has been e The oxygen sensor has been warm for at least used 100 seconds The oxygen sensor is determined to be warm by the ECU if ECT is greater than 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 65 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Diagnostic Aids Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure A poor connection rubbed through wire insulation or a wire broken inside the insulation may cause an intermittent Check the following conditions e A poor connection or a damaged harness Check for the following conditions Backed out terminals Improperly formed or damaged terminals Poor terminal to wire connection Damaged harness A poor ECU to the engine block ground Faulty Fuel Control Solenoid FCS Faulty Regulator Control Valve RCV Faulty Low Pressure Regulator Exhaust leaks If there is an exhaust leak the engine may pull the outside air into the exhaust and past the sensor e
93. nition Power HO2S B2 Si Signal B2S1 Ground HO2S Bank 1 Sensor 1 Circuit Description The ECU supplies a voltage of about 0 45 volt between the HO2S High and HO2S Low circuits The Heated Oxygen Sensor HO2S Bank 2 Sensor 1 varies the voltage within the range of about 1 0 1000 mV volt if the exhaust is rich down to about 0 1 100 mV volt if the exhaust is lean The sensor is like an open circuit and produces no voltage when it is below 360 C 600 F DTC 65 determines if the HO2S sensor or the circuit is shorted to high by checking for an extended rich condition This DTC is a type B DTC Conditions for Setting the DTC e The engine is running at greater than 500 RPM e The ECT is greater than 70 C 160 F e The oxygen sensor has been warm for at least 120 seconds The oxygen sensor is determined to be warm by the ECU if ECT is greater than 40 C 104 F and the mass air flow is above 17 g s for at least 120s Powertrain i bios ood Alternative Fuel Control I Engine Control B2 1 Module PCM Seed ow Unit AF ECU I T a rr C001 BLU Heated Oxygen Sensor HO2S 1 Bank 2 e The ECU is in closed loop operation e The HO2S Bank 2 Sensor 1 voltage is greater than 1 0 volt Action Taken When the DTC Sets The MIL will be turned on after 2 consecutive trips with test failures The system will operate in Open Loop if any DTC of the second HO2S Bank 1 Sensor 1 is se
94. not present operate the vehicle at different engine speeds and loads 4 This test determines if the ECU is the cause of DTC 42 10 This test will verify operation of the fuel control valves If the pressure reading is fluctuating this indicates proper operation of the fuel control valves The fuel control valves may function at one operating condition and fail at another operate the vehicle at varying engine speeds and loads to check for this condition 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 66 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 42 HO2S Insufficient Activity Bank 1 Sensor 1 Sep Aon O Vaws Yes No Was the Alternative Fuels AF Powertrain On Board Diagnostic OBD System Check performed Go to Step 2 1 Install a scan tool 2 Idle the engine at normal operating temperature 3 Operate the engine above 1200 RPM for two 300 mV to minutes 600 mV 4 Observe the H02S sensor reading on the scan Does the scan tool indicate the bank 1 HO2S 1 i i ifi voltage varying outside the specified range Go to Step 13 1 Disconnect the HO2S Bank 1 Sensor 1 sensor electrical connector 2 Install a jumper between the HO2S Bank 1 Sensor 1 harness high and low PCM side signal circuits 200 mV 3 Observe the H02S sensor reading on the scan Does the scan tool indicate the bank 1 HO2S 1 G Step 7 voltage less than the specified value o to Step Turn the ignition OFF Disc
95. ns at the ECU and IAT sensor by wiggling the connector gently and monitoring the IAT voltage on a DVOM connected to the ECU connector If the voltage waivers repair the connector that caused the condition 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 41 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Also a sensor may become skewed or mis scaled Important Use the same diagnostic test equipment The Temperature vs Resistance value table will for all of the measurements help to detect a skewed sensor Refer to Temperature vs Resistance 3 With the ECU connector disconnected and the voltage still present this eliminates the ECU as Test Description the possible cause of the fault 4 If the IAT sensor circuit voltage measures less The numbers below refer to the step numbers on the than 0 019 volts the conditions for the DTC diagnostic table are still present and the problem is not intermittent DTC 23 IAT Sensor Circuit Low Voltage Sep Adon Vale Yes Was the Alternative Fuels AF Powertrain On Board Go to AF Diagnostic OBD System Check performed Powertrain OBD System Go to Step 2 Check 1 Connect the scan tool 2 Turn the ignition ON leaving the engine OFF 3 Monitor the IAT sensor voltage Is the IAT sensor reading above the specified value Go to Step 3 Go to Step 4 1 Turn the ignition OFF 2 Disconnect ECU connector C001 3 Turn the ignition ON 139 C 282 F Does the scan tool d
96. o Step 4 Go to Step 3 Disconnect ECU connector C001 Disconnect ECT connector Using a DVOM check the resistance of the ECT signal circuit between the connectors Is the resistance below the specified value Reconnect all connectors Go to Step 5 Go to DTC PO117 ECT Sensor Circuit Low Voltage in the GM MD Service Go to Step 6 Manual 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 38 Is the action complete Allow the engine to cool completely Install the scan tool Turn ON the ignition Compare the IAT and the ECT The values should be close Are they close The circuit has high resistance inspect ECU connector C001 and ECT connectors for loose or corroded pins 2 Has the problem been corrected Go to Step 10 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM ation Value s No Verify that the heater defroster coolant valves are turned OFF Start the engine Note ECT at start temperature Run the engine while monitoring the ECT on the 45 F 25 C scan tool Does the ECT value increase steadily greater than Go to the above the specified value over the starting ECT Diagnostic value within 10 minutes Aids Go to Step 7 1 Turn OFF the ignition 2 Allow the engine to cool Go to Engine Cooling System in the GM MD is Us Go to Step 8 Go to Engine Cooling System in the GM MD Service Manual Go to Step 9 3 Check the cooling system coolant level Was a probl
97. oes the MIL begin to flash Observe and record any DTCs All DTCs will be flashed 3 times before proceeding to the next DTC All codes have been displayed when DTC 12 is flashed again Are any DTCs set Go to Data Link Connector Diagnosis in the GM MD Service Does the scan tool display the PCM data Go to Step 3 Manual 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 13 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Before going to the applicable DTC table while in AF ECU DTC retrieval mode turn ignition from OFF to ON 3 additional times and wait 10 seconds after the MIL turns off before turning ignition off This will clear all AF ECU DTCs and reset fuel trim Important If the ignition switch is not cycled OFF for 10 seconds after clearing any DTC s and the vehicle is started the AF ECU OBD system will be disabled for that key cycle Is the action complete Crank the engine for 10 seconds or until the engine starts Does the engine start Compare the scan tool engine data with the Typical Scan Tool Data Values Are values normal or within typical range Go to the Applicable DTC Table Go to Engine Cranks but Does Not Run in the GM MD Service Go to Step 8 Manual Go to the Go to indicated Driveabilit Component yton System checks 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 14 Website 5 29 03 Malfunction Indicator Lamp Circuit Circuit Description
98. of the HO2S This will be accompanied by lean shorted and the cause of the fault driveability conditions and a powdery white 8 This step will determine if the AF ECU is deposit on the sensor the cause of the fault e Faulty HO2S Bank 1 Sensor 1 If the HO2S 9 This test determines if the sensor wiring is Bank 1 Sensor 1 is internally shorted the the cause of the DTC 45 HO2S Bank 1 Sensor 1 voltage displayed will 10 DTC 45 HO2S Circuit High Voltage Bank 1 Sensor 1 Sep O Aion Vals No Was the Alternative Fuels AF Powertrain On Board Go to AF Diagnostic OBD System Check performed Powertrain OBD System Go to Step 2 Chack Install a scan tool Idle the engine at normal operating temperature Operate the engine above 1200 RPM for two minutes 300 mV to Observe the H02S sensor reading on the scan 600 mV tool Does the scan tool indicate the bank 1 HO2S 1 voltage varying outside the specified range Go to Step 8 Go to Step 3 1 Disconnect the HO2S Bank 1 Sensor 1 sensor electrical connector 2 Observe the H02S sensor reading on the scan 350 mV to tool 550 mV Does the scan tool indicate the bank 1 HO2S 1 voltage is within the specified range Go to Step 6 Go to Step 4 Turn the ignition OFF Disconnect ECU connector C001 Turn the ignition ON Observe the H02S sensor reading on the scan 350 mV to tool 550 mV Does the scan tool indicate the bank 1 HO2S 1 voltage within the specified range
99. ol Solenoid FCS Replacement 2 cce c ceeeeeceeeeeeeeeeeeeeeeeeeeeeeeeeeeeens 111 Idle Control Solenoid ICS Replacement eese 112 Regulator Control Valve RCV Replacement sscecceeeeeeeeeeeeeeeeeeeeseeeeeeeeeeeeeees 112 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 3 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Fuel Mixer Replacement esses seen ener nnne nnne nnn nnn nnn nnn 112 Fuel Mixer Outlet Elbow Replacement eee nnn 112 Engine Control Unit ECU Replacement eeeeeeeeeeenenenn nennen 112 Propane Fuel System Inspection eeeeeeeeeeeee eene nn nnne nn nnn 113 Technical Specifications ceeeeeeeieeee sees nn nnne nnn nnn 113 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 4 Website 5 29 03 VEHICLE APPLICATION IMPCO PROPANE FUEL SYSTEM The IMPCO propane system is designed for the 1999 and 2000 GM Medium Duty Chassis with the 7 4L V 8 PROPANE FUEL SYSTEM CAUTIONS CAUTION Do not smoke carry lighted tobacco or use a lighted flame of any type when working on or near any fuel related component Highly flammable air fuel mixtures may be present and can be ignited causing personal injury CAUTION Do not allow propane to contact the skin Propane is stored in the fuel tank as a liquid When propane contacts the atmos
100. olt between the HO2S high and HO2S low circuits The Heated Oxygen Sensor HO2S Bank 1 Sensor 1 varies the voltage within the range of about 1 0 volt 1000 mV if the exhaust is rich down to about 0 1 100 mV volt if the exhaust is lean The sensor is like an open circuit and produces no voltage when it is below 360 C 600 F DTC 45 determines if the HO2S sensor or the circuit is shorted to high by checking for an extended rich condition This DTC is a type B DTC Conditions for Setting the DTC e The engine is running at greater than 500 RPM e The ECT is greater than 70 C 160 F e The oxygen sensor has been warm for at least 120 seconds The oxygen sensor is determined to be warm by the ECU if ECT is greater than 40 C 104 F and the mass air flow is above 17 g sec for at least 120s e The ECU is in closed loop operation 015 TAN WHT p 2 4 p 0 2 24 i EGNI UTT Ip OBISI grs Control BISI pisi Engine Control 1 TER Uu 1 Signal Low Module PCM 1 Signal Low 1 Unit AF ECU i Circuit Fuse 1 1 1 i 1 Breaker i kir N E E eee a RST ATLA is ei ao i 1 Block 47 A Nemee 6N C2 BLU Nees C001 BLU TAN WHT 1653 Heated Oxygen Sensor HO2S 1 Bank 1 The HO2S Bank 1 Sensor 1 voltage is greater than 1 0 volt Action Taken When the DTC Sets The MIL will be turned on after 2 consecutive trips with test failures The system will operate in Open Loo
101. onnect ECU connector C001 Turn the ignition ON Observe the H02S sensor reading on the scan tool 200 mV Does the scan tool indicate the bank 1 HO2S 1 voltage less than the specified value Go to Step 14 1 Remove the jumper wire 2 Using a DVOM measure the voltage between the bank 1 HO2S 1 high signal circuit and a 375 mV to known good ground 525 mV Is the voltage within the specified range Go to Step 6 1 Disconnect the PCM connector 2 Using a DVOM check for continuity of the bank 1 HO2S 1 signal low circuit between the PCM and the HO2S connector 3 Check the bank 1 HO2S 1 low circuit for a short to ignition power or ground Was a problem found Go to Step 17 Go to AF Powertrain OBD System Check Go to Step 3 Go to Step 4 Go to Step 5 Go to Step 8 Go to Step 16 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 67 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Step Action Vales ves m 1 Remove the jumper wire 2 Using a DVOM measure the voltage between the bank 1 HO2S 1 high signal circuit and a 375 mV to known good ground 525 mV Is the voltage within the specified range Go to Step 9 Go to Step 8 1 Disconnect the PCM connector 2 Using a DVOM check for continuity of the bank Go to Step 17 Go to Step 16 Go to Step 17 Goto Step 10 1 HO2S 1 signal high circuit between the PCM and the HO2S connector 3 Check the bank 1 HO2S 1 high circuit for a short to ignition powe
102. onnection at the bank 2 HO2S 1 connector Check all connector circuit connections for loose terminal tension Install a test lamp between the bank 2 HO2S 1 heater high and low circuits the test lamp should illuminate Go to Step 15 Goto Step 10 Go to AF Fuel System Diagnosis Go to Step 11 Go to Step 19 Go to Step 12 Go to Step 19 EN Was a problem found Reconnect the HOS2 connector Connect a water column gauge or a manometer to the secondary test port of the low pressure regulator LPR Start the engine Observe the pressure gauge in the secondary test port Is the fuel pressure reading steady 1 Check for engine vacuum leakage Repair any leaks that are found 2 Check for exhaust system leakage upstream of the sensor Repair any leaks that are found Was a problem found and repaired Replace the bank 2 HO2S 1 Is the action complete DTCs displayed that have not been diagnosed applicable Go to Powertrain Diagnostic DTC table Aids Go to Step 17 Goto Step 15 Go to Step 19 Go to Step 17 Goto Step 18 Go to Step 19 Go to Step 19 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 82 Check for a poor connection at the ECU Was a problem found Replace the ECU Refer to ECU Replacement Is the action complete Check for a faulty or loose connection at the PCM connector Was a problem found Repair the circuit as necessary Is the action complete Replace the PCM Im
103. or PCM DTCs displayed that have not been diagnosed Go to the applicable DTC table System OK 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 47 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 31 ETC System Fault Circuit Description If a PCM Throttle Actuator Control TAC DTC P1514 P1515 P1516 or P1518 is detected by the AF ECU it will set DTC 31 and enter ETC Fault Mode In this mode the AF ECU issues a command to de energize the ETC solenoid The air valve vacuum in the mixer is vented to atmosphere causing the air valve to close and reduce airflow through the mixer to a default limit value 6 g s 9 g s This forces an idle condition The AF ECU commands the idle control solenoid ICS to fuel the engine and maintain fuel control This DTC is a type A DTC Conditions for Setting the DTC The following conditions will set the DTC e The PCM has initiated a reduced power mode due to a TAC system failure DTCs P1514 P1515 P1516 P1518 Action Taken When the DTC Sets The ECU will set DTC 31 and illuminate the MIL light after 1 fault has occurred The ECU will initiate reduced power mode by closing the mixer air valve Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F from the
104. or damaged terminals 11 A voltage reading of less than 4 volts or Poor terminal to wire connection over 6 volts at the MAF signal circuit e Amis routed harness Inspect the MAF sensor indicates a fault in the wiring or a poor harness in order to ensure it is not routed too connection close to high voltage wires such as spark plug 12 This step verifies that the ignition feed leads circuit voltage and a good ground are e A damaged harness Inspect the wiring harness available at the MAF sensor for damage If the harness is OK observe the DTC 36 MAF Sensor Circuit Low Frequency Step Action Value s Was the Alternative Fuels AF Powertrain On Board Go to AF Diagnostic OBD System Check performed Powertrain OBD System Go to Step 2 Check 1 Start the engine 2 With the engine idling monitor the MAF frequency display on the scan tool 2 g s Is the MAF frequency below the specified value Go to Step 10 Go to Step 3 1 Using a DVOM set to read frequency back probe the MAF circuit in the ECU connector 2 With the engine idling monitor the MAF circuit 1 33 kHz frequency on the DVOM Is the MAF frequency below the specified value Go to Step 5 Go to Step 4 Operate the vehicle within the conditions for setting this DTC as specified in the supporting text Check to see if the MIL light illuminates Go to Diagnostic Did the MIL illuminate Go to Step 7 Aids Turn OFF the engine Disconnect ECU connector C003 Star
105. p 3 1 Disconnect the HO2S Bank 2 Sensor 1 sensor electrical connector 2 Observe the H02S sensor reading on the scan 350 mV to tool 550 mV Does the scan tool indicate the bank 2 HO2S 1 Go to Step 6 Go to Step 4 voltage is within the specified range Turn the ignition OFF Disconnect ECU connector C001 Turn the ignition ON 350 mV to Observe the H02S sensor reading on the scan 950 mV tool Does the scan tool indicate the bank 2 HO2S 1 voltage within the specified range Go to Step 9 Go to Step 5 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 85 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Step Action Vale 1 Disconnect the PCM connector 2 Using a DVOM check for continuity of the bank 2 HO2S 1 signal high circuit between the PCM ECU and the HO2S connector 3 Check the bank 2 HO2S 1 high circuit for a short to voltage or ground ves Ne Go to Step 12 Go to Step 11 Go to Step 12 Go to Step 7 Go to Step 14 Lom Was a problem found 1 Check for a poor terminal connection at the bank 2 HO2S 1 connector Check all circuits for loose terminal tension 2 Install a test lamp between the bank 2 HO2S 1 heater high and low circuits the test lamp should illuminate Was a problem found Replace the bank 2 HO2S 1 Is the action complete Check for a poor connection at the ECU Was a problem found Replace the ECU Refer to ECU Replacement Go to Step 1
106. p 5 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 89 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Step Acion Vae Disconnect the PCM connector Using a DVOM check for continuity of the bank 2 HO2S 1 signal high circuit between the PCM ECU and the HO2S connector Check the bank 2 HO2S 1 high circuit for a short to voltage or ground Check the bank 2 HO2S 1 low circuit for a short to voltage or ground Was a problem found ves Ne Go to Step 12 Go to Step 11 Go to Step 12 Go to Step 7 Go to Step 14 HN Check for a poor terminal connection at the bank 2 HO2S 1 connector Check all circuits for loose terminal tension Install a test lamp between the bank 2 HO2S 1 heater high and low circuits the test lamp should illuminate Was a problem found Replace the bank 2 HO2S 1 Is the action complete Check for a poor connection at the ECU Go to Step 12 Go to Step 10 Go to Step 14 EN Go to Step 12 Go to Step 13 Go to Step 14 Go to Step 14 gt 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 90 Was a problem found Replace the ECU Refer to ECU Replacement Is the action complete Check for a faulty or loose connection at the PCM connector Was a problem found Repair the circuit as necessary Is the action complete Replace the PCM Important If the PCM is faulty reprogram the PCM Refer to PCM Replacement P
107. p if any DTC of the second HO2S Bank 2 Sensor 1 is set DTC 63 64 or 65 Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F from the start up coolant temperature and the engine coolant temperature exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 74 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM be over 1V Try disconnecting the HO2S Bank Diagnostic Aids 1 Sensor 1 if the displayed voltage goes from over 1000 mV to around 450 mV replace HO2S Always diagnose ANY PCM codes that are present Bank 1 Sensor 1 before beginning this diagnostic procedure e Never solder the HO2S wires Check the following items Test Description e Fuel pressure The ECU can compensate for small increases in fuel pressure However large The numbers below refer to the step numbers on the increases in fuel pressure may set a DTC diagnostic table e Faulty Fuel Control Solenoid FCS e Vacuum leaks in the fuel control valve hoses 6 This step will determine if the fault is e Faulty Regulator Control Valve RCV currently present e False rich indication due to silicon contamination 7 This step will determine if the HO2S is
108. pen Verify that liquid fuel not vapor is being delivered to the LPR Verify that the correct PCM software is installed Sensor Checks Check the Heated Oxygen Sensor HO2S for contamination and performance Refer to Heated Oxygen Sensor in the GM MD Service Manual Check for proper operation of the MAP sensor Check for proper operation of the ECT sensor Check EGR system for proper operation Exhaust System Checks Check the exhaust system for a possible restriction Inspect the exhaust system for damaged or collapsed pipes Inspect the muffler for signs of heat distress or for possible internal failure Check for possible plugged catalytic converter Refer to Restricted Exhaust System Diagnosis or Exhaust System in the GM MD Service Manual Engine Mechanical Check Check the engine for the following e Engine compression e Valve timing e Improper or worn camshaft Refer to Engine Mechanical in the GM MD Service Manual 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 99 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Additional Check Website 5 29 03 Check the Control Module grounds for being clean tight and in their proper locations Check for an Intermittent EGR problem Refer to EGR System Diagnosis in the GM MD Service Manual Check the A C operation Refer to A C Compressor Clutch Control Diagnosis in the GM MD Service Manual Check for proper Torque Converter Clutch TCC operation
109. phere it immediately expands into a gas resulting in refrigeration that can cause severe burns CAUTION Do not allow propane to accumulate in areas below ground level such as in a service pit or under an alignment rack Propane is heavier than air and can displace oxygen creating a dangerous condition DESCRIPTION AND OPERATION PROPANE FUEL SYSTEM The primary components of the propane fuel system are the low pressure regulator fuel mixer electric lock off solenoids and engine control unit ECU The system operates at pressures up to 312 psi Propane is delivered from the tank through the filter underbody low pressure lock off LPL assembly to the underhood LPL Both lock offs are activated by the fuel pump control circuit The lock offs which are normally closed open only when the engine is cranking or running Fuel passes through the underhood lock off solenoid to the fuel inlet on the LPR Propane enters the primary chamber of the LPR through the primary jet where the pressure is reduced to approximately 1 2 psi 1999 or approximately 2 3 psi 2000 This fuel is then vaporized as it passes through the heat exchanger located in the center of the regulator During normal engine operation the fuel is drawn from the secondary chamber of the regulator by the vacuum created as the air passes through the fuel mixer This pressure drop is most commonly referred to as air valve vacuum As the air valve vacuum increases o
110. plement Page 16 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Step Action Value s 1 Allow engine to idle until normal operating temperature is reached 2 Checkif there are any DTCs set Go to the Are any DTCs displayed that have not been Applicable diagnosed DTC Table System OK 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 17 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM AF Fuel System Diagnosis Secondary Pressure Test Port Fuel System Description The alternative fuel engine control unit AF ECU receives information from various engine sensors in order to control the operation of the fuel and idle control valves and the low pressure lock off LPL solenoids The LPL solenoids prevent fuel flow unless the engine is cranking or running LPG is stored in the tank and delivered under pressure to the System as a liquid During key on the underbody LPL receives a two 2 second prime pulse When the key is ON and the engine running LPG flows from the tank through the underbody LPL fuel filter and fuel lines at pressures up to 2151 kPa 312 psi The fuel then flows to the underhood LPL and to the low pressure regulator LPR where the fuel is vaporized and the pressure reduced in two stages The first stage reduces the pressure to approximately 1 to 2 psi 1999 or to approximately 2 3 psi 2000 The second stage reduces the pressure to approximately negative 1 5 w c The fuel
111. portant If the PCM is faulty reprogram the PCM Refer to PCM Replacement Programming The 7 4L LPG fuel system requires a unique PCM software calibration The DTC is intermittent Are there any Powertrain Ee Go to the Is the action complete Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Sep Aen wo e no Bring the engine up to normal operating temperature Run the engine above the specified value for at least 4 minutes Turn OFF the engine and the ignition for at 1500 RPM least 10 seconds Run the engine above the specified value for at least 4 minutes second time Did the MIL illuminate OX EPE p suelo OK 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 83 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 64 HO2S Circuit Low Voltage Bank 2 Sensor 1 Hot in Run And Start acra cip ret de E HO2S EGN IP B2 1 Circuit Fuse 1 i 1 l Signal I i Breaker 1 1 1 I HO2S Bank 1 Sensor 1 ignition Power HO2S B2 Si Signal B2S1 Ground HO2S Bank 1 Sensor 1 Circuit Description The ECU supplies a voltage of about 0 45 volt between the HO2S High and HO2S Low circuits The Heated Oxygen Sensor HO2S Bank 2 Sensor 1 varies the voltage within the range of about 1 0 volt if the exhaust is rich down to about 0 1 volt if the exhaust is lean The sensor is like an open circuit and produces no voltage when it is below 360 C 600 F DTC 64 determines if the HO2
112. r 1 Refer to DTC 42 HO2S Insufficient Activity Bank 1 Sensor 1 Refer to DTC 64 HO2S Circuit Low Voltage Bank 2 Sensor 1 Refer to DTC 65 HO2S Circuit High Voltage Bank 2 Sensor 1 Refer to DTC 63 HO2S Insufficient Activity Bank 2 Sensor 1 Fuel System Checks Check for Rich or Lean symptom that causes the condition Drive the vehicle at the speed of the complaint Monitoring the oxygen sensors will help identify the problem Check the fuel pressure while the condition exists Refer to AF Fuel System Diagnosis Verify proper regulator control valve operation Verify proper fuel control solenoid operation Verify that the LPG manual shut off valve is fully open Check the in line fuel filter for restrictions Ignition System Checks Check for the proper ignition output voltage using the spark tester J26792 or the equivalent Refer to Enhanced Ignition System in the GM MD Service Manual Check the spark plugs Remove the plugs and inspect them for the following conditions Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Check the Crankshaft Position CKP sensor Refer to DTC P0336 CKP Sensor Circuit Performance in the GM MD Service Manual 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 106 Website 5 29 03 Additional Check Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Check the Control Module grounds for being clean tight and in their proper locations Check the generator
113. r a faulty connection at the MAP sensor Was a problem found Check for an open MAP signal circuit Was a problem found Check the MAP sensor signal circuit for a short to ground Was a problem found Check for an open in the MAP sensor 5 volt reference circuit Was a problem found Replace the MAP sensor Is the action complete Repair the circuit as necessary Is the action complete Value s Go to Step 18 5 0 V Go to Step 11 iu Go to Step 14 Go to the Applicable DTC Table Go to Step 16 Go to Step 16 Go to Step 16 Go to Step 16 Go to Step 18 Go to Step 18 Go to Step 9 Go to Step 12 Go to Diagnostic Aids Go to Step 15 Go to Step 13 Go to Step 17 Go to Step 17 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 52 Website 5 29 03 SPC PROPANE FUEL SYSTEM _ PROPANE FUEL SYSTEM Value s Replace the PCM Important If the PCM is faulty reprogram the PCM Refer to PCM Replacement Programming The 7 4L LPG fuel system requires a unique PCM software calibration 2 Is the replacement complete Go to Step 18 Operate the vehicle within the conditions for setting this DTC as specified in the supporting text 2 Check to see if the MIL light still illuminates Did the diagnostic run and pass Go to Step 19 Go to Step 2 Go to the Are any ECU or PCM DTCs displayed that have not applicable DTC been diagnosed Table System OK 1999 2000 GM Medium Duty Cha
114. r decreases the amount of fuel drawn from the secondary chamber will increase or decrease In the fuel mixer the propane vapor is combined with air to form a combustible air fuel mixture The fuel system is controlled by the Alternative Fuels Engine Control Unit AF ECU The AF ECU receives input from various engine sensors to determine the amount of fuel necessary to maintain a precise air fuel mixture across the entire engine operational range The AF ECU then sends a command to the fuel control solenoid FCS to meter the appropriate quantity of fuel The FCS meters the fuel flow by changing the pressure on the regulator diaphragm from atmosphere to vacuum The system will also automatically sense and compensate for changes in altitude LOW PRESSURE REGULATOR LPR The IMPCO Model E low pressure regulator LPR is a combined pressure regulator and vaporizer The regulator is a negative pressure two stage configuration that is closed when the engine is not running When the engine is cranking or running a partial vacuum is created in the fuel line to the regulator This opens the regulator permitting fuel to flow to the fuel mixer The regulator receives liquid fuel at tank pressure The pressure is reduced in two stages to slightly less than atmospheric In the first stage the pressure is reduced to approximately 1 2 psi 1999 or approximately 2 3 psi 2000 Also during this stage the liquid fuel is vaporized by heating t
115. r equivalent Duty Cycle Monitoring Tool e IMPCO Fuel System Analyzer FSA or DVOM GM J 39200 Fluke 88 or equivalent Diagnostic Scan Tool e GM Tech 2 or equivalent Pressure Gauges e Water Column Gauge Manometer GM 7333 6 or equivalent e 0 5 PSI Gauge GM 42580 or equivalent Test Description 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 24 Website 5 29 03 The numbers below refer to step numbers on the diagnostic table 4 This test determines proper fuel control system authority at idle 6 This test determines if there is a ETC system problem 7 This test determines proper fuel control system operation at 2500 RPM 10 This determines if there is an RCV problem at idle 14 This determines if there is an RCV problem at 2500 RPM IMPCO PROPANE FUEL SYSTEM AF Fuel Control System Diagnosis Sep Adon O Vaw g Yes Me Go to Step 2 1 Were you referred to this procedure by another diagnostic chart Go to Step 3 Perform the AF On Board Diagnostic OBD System Check Go to the applicable Are any DTCs present in the AF ECU DTC Table Go to Step 3 Go to AF Fuel System Has the AF Fuel System Diagnosis been performed Go to Step 4 Diagnosis 1 Connect a scan tool 2 Start the engine and allow it to reach operating temperature 3 Connect a duty cycle monitoring tool at C011 test connector as follows FSA Yellow clip to pin A YEL Green clip to pin B P
116. r gallon 60 F esanian mener 4 243 iunio 6 3 BTU per gallon VaporiZed reine e a E E He 91 500 ehe 123 000 BTU per pound vaporized ssseseeee Hem 21 5605 c iren 20 500 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 113 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM PRESSURE CONVERSION CHART MULTIPLY Inches of Ounces Per Inches of Pounds Per 3 Water Square Mercury Square od OBTAIN Column Inch Column Inch Inches of By 1 731 13 6 27 7 Water Column W Ounces Per Square 578 By 7 16 Inch V 85 Inches of Mercury 0 0736 0 128 By Column Pounds Per v 0 0361 0625 0 491 Square Inch By 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 114 Website 5 29 03
117. r itself Refer to DTC P1115 ECT Sensor CKT Intermittent High Voltage Diagnostic Aids or DTC P0118 ECT Sensor Circuit High Voltage Diagnostic Aids in the GM MD Service Manual Check the Manifold Absolute Pressure MAP sensor response and accuracy Fuel System Checks Check for Rich or Lean symptom that causes the condition Drive the vehicle at the speed of the complaint Monitoring the oxygen sensors will help identify the problem Verify proper operation of the idle control solenoid Verify proper operation of the fuel control valve solenoid Verify proper operation of the regulator control valve Perform a cylinder compression test Refer to Engine Mechanical in the GM MD Service Manual Check for leaking fuel injectors While the injectors are not used they provide a possible vacuum leak point Verify that the injector fuel rail plugs are in place Check the fuel pressure Refer to the AF Fuel System Diagnosis Check mixer module assembly for proper installation and connection 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 103 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Check for the proper ignition output voltage using the spark tester J26792 or the equivalent Refer to Ignition System Diagnosis in the GM MD Service Manual Check the spark plugs Remove the plugs and inspect them for the following conditions Wet plugs Cracks Wear Improper gap Burned electrodes Blistered insulators Heavy
118. r or ground Was a problem found 1 Check for a poor terminal connection at the bank 1 HO2S 1 connector Check all connector circuit connections for loose terminal tension 2 Install a test lamp between the bank 1 HO2S 1 heater high and low circuits the test lamp should illuminate Was a problem found 1 Check for engine vacuum leakage Repair any leaks that are found 2 Check for exhaust system leakage upstream of the sensor Repair any leaks that are found Was a problem found and repaired Go to Step 19 Go to Step 12 Go to Step 19 Dus Go to the applicable Go to Powertrain Diagnostic DTC table Aids Go to Step 17 Goto Step 15 Go to Step 19 D 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 68 Replace the bank 1 HO2S 1 Is the action complete The DTC is intermittent Are there any Powertrain DTCs displayed that have not been diagnosed Check for a poor connection at the ECU Was a problem found Replace the ECU Refer to ECU Replacement 1 Reconnect the HOS2 connector 2 Connect a water column gauge or a manometer to the secondary test port of the low pressure regulator 3 Start the engine 4 Observe the pressure gauge in the secondary test port Go to AF Fuel System Is the fuel pressure reading steady Diagnosis Go to Step 11 Is the action complete Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Sep Adon vawe Ye mw Check for a faulty or loos
119. ramming The 7 4L LPG fuel system requires a unique PCM software calibration Is the action complete The DTC is intermittent Are there any Powertrain Go to the DTCs displayed that have not been diagnosed applicable Go to Powertrain Diagnostic DTC table Aids Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Sep Aon 1 Vawgj Yes Ne Bring the engine up to normal operating temperature Run the engine above the specified value for at least 4 minutes Turn OFF the engine and the ignition for at least 1500 RPM 10 seconds Run the engine above the specified value for at least 4 minutes second time Did the MIL illuminate QOTSA SYSTE 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 77 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 58 AF ECU Internal Failure Diagnostic Aids Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure A poor connection a rubbed through wire insulation or a wire broken inside the insulation may cause an Multiple Stored Codes Intermittent connections may cause the AF ECM to store multiple false codes If the AF ECM has stored an excessive number of DTCs for no apparent intermittent reason check the battery and ignition power and ground circuits to the AF ECM Check for the following conditions e A poor connection or damaged harness Inspect the ECM harness connector for the following conditions Backed
120. rate the vehicle at different engine speeds and loads 4 This test determines if the ECU is the cause of DTC 63 10 This test will verify operation of the fuel control valves If the pressure reading is fluctuating this indicates proper operation of the fuel control valves The fuel control valves may function at one operating condition and fail at another operate the vehicle at varying engine speeds and loads to check for this condition DTC 63 HO2S Insufficient Activity Bank 2 Sensor 1 Was the Alternative Fuels AF Powertrain On Board Diagnostic OBD System Check performed Value s Go to AF Powertrain OBD System heck Go to Step 2 one Install a scan tool Idle the engine at normal operating temperature 300 mV to Operate the engine above 1200 RPM for two 600 mV minutes Observe the H02S reading on the scan tool Does the scan tool indicate the bank 2 HO2S 1 voltage varying outside the specified range Go to Step 13 Go to Step 3 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 80 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Step Action Vale Yes mo Disconnect the HO2S Bank 2 Sensor 1 sensor electrical connector Install a jumper between the HO2S Bank 2 Sensor 1 harness high and low PCM side signal circuits 200 mV Observe the H02S sensor reading on the scan tool Does the scan tool indicate the bank 2 HO2S 1 voltage less than the specified value
121. re 37 DTC 23 IAT Sensor Circuit Low Voltage eeeeeeeeeeee ener nnne nnn 41 DTC 25 IAT Sensor Circuit High Voltage eere 44 DTC 31 ETC System Fault eeeeseseeeeeeeseeeeeeesee enne nennen nnne nnne nennen nn 48 DTC 34 MAP Sensor Circuit Low Voltage eeeeeeeereeenene ener 50 DTC 36 MAF Sensor Circuit Low Frequency eene nennen nennen 54 DTC 37 MAF Sensor Circuit High Frequency eere 58 DTC 41 CKP Sensor Circuit Performance eeeeeeeeee eren 62 DTC 42 HO2S Insufficient Activity Bank 1 Sensor 1 eee 65 DTC 44 HO2S Circuit Low Voltage Bank 1 Sensor 1 eene 70 DTC 45 HO2S Circuit High Voltage Bank 1 Sensor 1 eere 74 DTC 58 AF ECU Internal Failure eeeeeeeeeeeeeeee enne nennen nennen nnn nnn 78 DTC 63 HO2S Insufficient Activity Bank 2 Sensor 1 eene 79 DTC 64 HO2S Circuit Low Voltage Bank 2 Sensor 1 eene 84 DTC 65 HO2S Circuit High Voltage Bank 2 Sensor 1 eere 88 Symptom DIgn sSiS ie 92 Important Preliminary CHeCKS ccccceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeneeseeeeeeeseeeeeeeseeneeees 92 Intermittents E fecse det icebdgectacesshyiccuczesiecseanttecbegetsccacesstacecses ecde
122. rogramming The 7 4L LPG fuel system requires a unique PCM software calibration Is the action complete The DTC is intermittent Are there any Powertrain Go to the DTCs displayed that have not been diagnosed applicable Go to Powertrain Diagnostic DTC table Aids Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Sep Aon 1 Vawgj Yes Ne Bring the engine up to normal operating temperature Run the engine above the specified value for at least 4 minutes Turn OFF the engine and the ignition for at least 1500 RPM 10 seconds Run the engine above the specified value for at least 4 minutes second time Did the MIL illuminate QOTSA SYSTE 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 91 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Symptom Diagnosis Important Preliminary Checks Before Using This Section Before using this section you should have performed AF Powertrain On Board Diagnostic Check and determined that 1 The Control Module and MIL Malfunction Indicator Lamp are operating correctly 2 There are no Diagnostic Trouble Codes DTCs stored or a DTC exists but without a MIL Several of the following symptom procedures call for a careful visual and physical check The visual and physical checks are very important The checks can lead to correcting a problem without further checks that may save valuable time Visual and Physical Checks Check all ECU and PCM system fus
123. rom the start up coolant 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 58 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM temperature and the engine coolant temperature exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used Diagnostic Aids Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure Check for the following conditions e A poor connection at the ECU or MAF sensor Inspect harness connectors for the following conditions Backed out terminals Improper mating Broken locks Improperly formed or damaged terminals Poor terminal to wire connection A mis routed harness Inspect the MAF sensor harness in order to ensure it is not routed too close to high voltage wires such as spark plug leads A damaged harness Inspect the wiring harness for damage If the harness appears to be okay observe the scan tool while moving the connectors and the wiring harnesses related to the MAF sensor A change in the display indicates the location of the fault Test Description The numbers below refer to the step numbers on the diagnostic table 2 This step verifies that the problem is present at idle 9 A frequency reading with the MAF sensor connector disconnected indicates an Electromagnetic Interference EMI related fault or a poor connection DTC 37 MAF Sensor Circuit High Frequency Sep Ado
124. s MAF sensor produces a frequency signal that can be monitored using a scan tool The frequency varies within a range of around 5 to 10 g s at idle This DTC sets if the signal from the MAF sensor measures above the possible range of a normally operating MAF sensor This DTC is a type A DTC Conditions for Setting the DTC Ignition On Engine Off Test e Ignition is ON and the engine is OFF e Battery voltage is greater than 10 volts e MAF frequency is greater than 10 39 kHz 331 g s for 0 5 second 4B C1 RED Powertrain g Alternabye Fue Control Engine Control Module PCM Unt AF ECU C001 BLU Air Flow MAF Cranking Test e Engine is cranking e The battery voltage is greater than 8 volts e MAF frequency is greater than 10 39 kHz 331 g s for 0 5 second Running High Frequency Test e Engine run time is greater than 10 seconds Battery voltage is greater than 10 volts e Engine is running at greater than 500 RPM MAF frequency is greater than 10 39 kHz 331 g s for 0 5 second Action Taken When the DTC Sets If a MAF high input fault is detected the ECU will set DTC 37 and illuminate the MIL light after 1 fault has occurred Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F f
125. secondary test port will be approximately 1 0 to 2 0 w c If the vehicle has a hard start or poor idle check for proper operation of the idle control solenoid ICS 6 This step checks the base mechanical LPR output pressure by disabling all fuel control devices 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 18 IMPCO PROPANE FUEL SYSTEM 9 This step checks for proper air valve 19 This determines if fuel is available from the 1 Were you referred to this procedure by a DTC diagnostic chart operation fuel tank supply system AF Fuel System Diagnosis Value s Go to Step 3 Go to Step 2 Go to the applicable DTC Are any DTCs present in the AF ECU Table Go to Step 3 Verify that the LPG fuel tank has a minimum of 1 4 tank of fuel Does the vehicle have fuel Go to Step 4 1 Connect a water column gauge or a manometer to the secondary test port of the low pressure Go to Step 5 Go to Step 8 With the engine at 2500 rpm observe the pressure reading for the LPR secondary pressure 1 25 to 1 75 w c Does the fuel pressure fluctuate rhythmically outside the specified range Goto Step 29 Goto Step 6 Perform the AF On Board Diagnostic OBD System Check regulator LPR 2 Start the engine and allow it to reach operating temperature Does the engine start and run 1 Remove the vacuum hose from the LPR fitting 2 Disconnect the ICS electrical connector Note This action may cause a DT
126. spect the hoses between the ETC solenoid and the mixer for leakage and proper connection Check the mixer cover for proper installation and condition Was a problem found and repaired Replace the Fuel Control Solenoid FCS Refer to Fuel Control Solenoid FCS Replacement Is the action complete Replace the ETC Solenoid Refer to ETC Solenoid Replacement Repair the open or damaged circuit Is the action complete Go to Step 36 Is the action complete Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Step Action Values ve m 1 Return the fuel system to normal operating condition 2 Observe the scan tool MAF reading 3 Raise the engine speed to approximately 2500 RPM or greater than 28 g s MAF 25 to 75 4 Observe the duty cycle reading of the FCS Is the FCS duty cycle within the specified range GOD SIE SA sed o to Step o to Step Check all vacuum hoses and mixer connections for leakage Goto Step 36 Go to Step 33 Go to Step 36 Was a problem found and repaired Replace the fuel mixer Refer to Fuel Mixer Replacement Is the action complete Replace the PCM Important If the PCM is faulty reprogram the PCM Refer to PCM Heplacement Programming The 7 4L LPG fuel system requires a unique PCM software calibration Is the action complete Disconnect all test equipment Start the engine Using SNOOP or equivalent leak check any fuel system repairs made Is the action complete
127. ssis Service Manual Supplement Page 53 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 36 MAF Sensor Circuit Low Frequency MAF L L Hot in Run And Start 1 Sensor Signal IGN RLY VIM IP PROT Naa PESESES Circuit 48 Breaker Ignition Power MAF Sensor Signal Ground B BLK 451 B C008 BLK 451 Powertrain Control 1 Module PCM i Signal 1 wet ep ee ee eee ens Alternative Fuel Engine Control Unit AF ECU L MAF Sensor 1 L i C001 BLU 492 Air Flow MAF Sensor Circuit Description The Mass Air Flow MAF sensor measures the amount of air entering the engine during a given time The ECU uses the MAF information for fuel delivery calculations A large quantity of air entering the engine indicates an acceleration or high load situation A small quantity of air indicates deceleration or idle This MAF sensor produces a frequency signal that can be monitored using a scan tool The frequency varies within a range of around 5 to 10 g s at idle This DTC sets if the signal from the MAF sensor measurers below the possible range of a normally operating MAF sensor This DTC is a type A DTC Conditions for Setting the DTC Cranking Test e The engine is cranking e The battery voltage is greater than 8 volts e MAF frequency is below 125 Hertz 1 g s for 0 5 second Running Low Frequency Test e Engine run time is greater than 10 seconds Battery vol
128. start up coolant temperature and the engine coolant temperature exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used Diagnostic Aids Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure A poor connection a rubbed through wire insulation or a wire broken inside the insulation may cause an intermittent Check for the following conditions e A poor connection or damaged harness Inspect the ECU harness connector for the following conditions Backed out terminals Improper mating Broken locks Improperly formed or damaged terminals Poor terminal to wire connection and Damaged harness e The intermittent test If the connections and the harness check OK monitor a DVOM connected to the ECU terminal while moving the related connectors and the wiring harness If the failure is induced the voltage reading changes This may help isolate the location of the malfunction Test Description The numbers below refer to the step numbers on the diagnostic table 2 This test verifies that a PCM DTC has caused DTC 31 to be set by the AF ECU 3 This test checks the ETC circuit between the PCM and ECU DTC 31 ETC System Fault Sep Ado Vau Yes No Was the Alternative Fuels AF Powertrain On Board Diagnostic OBD System Check performed Go to AF Powertrain OBD System Check Go to Step 2 Se 2 Were PCM codes P
129. t DTC 42 44 or 45 Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F from the start up coolant temperature and the engine coolant temperature exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 88 Website 5 29 03 Diagnostic Aids Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure IMPCO PROPANE FUEL SYSTEM be over 1V Try disconnecting the HO2S Bank 2 Sensor 1 if the displayed voltage goes from over 1000 mV to around 450 mV replace HO2S Bank 2 Sensor 1 Check the following items e Never solder the HO2S wires e Fuel pressure The ECU can compensate for Test Description small increases in fuel pressure However large increases in fuel pressure may set a DTC Faulty Low Pressure Regulator The numbers below refer to the step numbers on the diagnostic table e Faulty Fuel Control Solenoid FCS e Vacuum leaks in the fuel control valve hoses 15 This step will determine if the fault is e Faulty Regulator Control Valve RCV currently present l e False rich indication due to silicon contamination 16 This step will determine if the HO2S is of the HO2S Th
130. t can be isolated to the PCM ignition feed the battery feed a poor PCM ground at the engine block or the PCM 5 A MIL that responds correctly to the scan tool commands indicates that a PCM fault is not present at this time or that the condition has been corrected 6 A MIL that responds correctly to the AF ECU DTC retrieval sequence indicates that the fault is not present or that the condition has been corrected Malfunction Indicator Lamp Circuit Step Action Value s Were you sent here by the Alternative Fuels AF Powertrain On Board Diagnostic OBD System Check Go to Step 3 Go to Step 3 Go to Step 2 Go to AF Powertrain OBD System Check Was the Alternative Fuels AF Powertrain On Board Diagnostic OBD System Check performed Attempt to start the engine Does the engine start 1 Connect a scan tool 2 Command the MIL on and off Go to Step 5 Go to Step 13 Go to Step 6 Go to Step 7 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 15 1 Turn the engine OFF for 15 seconds 2 Turn the ignition ON engine OFF Does the MIL illuminate for 2 seconds and then turn off Go to Step 6 Go to Step 4 Does the mil operate as commanded Website 5 29 03 IMPCO PROPANE FUEL SYSTEM ation Vae Turn the ignition OFF for 10 seconds 2 Turn the ignition switch from the OFF to RUN position 3 times within 10 seconds Does the MIL begin to flash Go to Step
131. t the engine 2 g s With the engine idling monitor the MAF frequency display on the DVOM Is the MAF frequency below the specified value Go to Step 6 Go to Step 8 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 55 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM tion Values Turn OFF the engine Disconnect the MAF sensor Using a DVOM check the resistance of the MAF circuit between the connectors ves m Go to Step 10 Go to Step 18 Go to Step 8 Go to Step 18 Go to Step 18 Go to Step 9 Go to Step 21 Is the resistance below the specified value Disconnect the MAF sensor Disconnect ECU connector C003 Using a DVOM check the resistance of the MAF circuit between the connectors Is the resistance below the specified value Check for a poor connection at the MAF sensor Check for a poor connection at the ECU connector If a poor connection is found replace the faulty terminal Did you find a poor connection Replace the ECU Refer to ECU Replacement Is the action complete 1 Turn OFF the ignition 2 Disconnect the MAF sensor connector 3 Turn ON the ignition leaving the engine OFF 4 Using a DVOM measure the voltage between the MAF signal circuit and battery ground Go to Step 12 Goto Step 15 Go to Step 14 Go to Step 13 Go to Step 16 Goto Step 17 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 56 Is the voltage near the specified value
132. tage is greater than 10 volts Engine is running at greater than 500 RPM MAF frequency is below 1 33 kHz 2 43 g s for 0 5 second Action Taken When the DTC Sets If a MAF low input fault is detected the ECU will set DTC 36 and illuminate the MIL light after 1 fault has occurred Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F from the start up coolant temperature and the engine coolant temperature exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 54 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Diagnostic Aids scan tool while moving the connectors and the wiring harnesses related to the MAF sensor A Always diagnose ANY PCM codes that are present change in the display indicates the location of before beginning this diagnostic procedure the fault Check for the following conditions Test Description e A poor connection at the ECU or MAF sensor Inspect harness connectors for the following The numbers below refer to the step numbers on the conditions diagnostic table Backed out terminals Improper mating 3 This step verifies the problem is present at Broken locks idle Improperly formed
133. tem at each serviced fitting ENGINE CONTROL UNIT ECU REPLACEMENT Removal Procedure 1 Disconnect the negative battery cable 2 Remove the ECU from the adapter bracket 3 Disconnect the ECU electrical connectors 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 112 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Installation Procedure 1 Connect the ECU electrical connectors 2 Install the ECU in the adapter bracket 3 Connect the negative battery cable PROPANE FUEL SYSTEM INSPECTION Inspect the propane fuel system hoses and vacuum lines for cracks wear or other damage Replace if necessary Inspect the propane fuel system brackets for cracks deformation or other damage Replace if necessary Inspect all fasteners and service as necessary TECHNICAL SPECIFICATIONS Electric Lock off Solenoid La ferisieelle cicce e MR Maximum 312 PSI Nominal Operating Voltage ssssesssseeeeeeeen mee nene mene nne nre 12 16 volts DC nominal Gollimpedarice s ta iecit E PEE Seana behing gz wsang nce esaes itera bte FE rb E een T 6 2 10 Ohms Working Temperature exco aeter Pe Ee eie OL DET LIS COLERE Ea A RR COLE CR RR EAD AA OE Pe dal 40 to 250 F Typical Operation at 40 F Maximum Voltage required to open Main Valve sse emen 5 5 volts DC DN fer BPI UE TIE 5 amps Maximum Coll Amperage sis nce t Set I SG EE SERE Uee ERR Qe SG ERN RE ANE
134. ting temperature 85 C to 95 C the voltage measures about 1 5 to 2 0 volts The AF ECU receives coolant temperature directly from the ECT signal circuit This DTC is a type B DTC Conditions for Setting the DTC The following conditions will set the DTC e The engine has been running longer than 5 seconds e ECT circuit voltage is less than 0 019 volts a ei Powertrain Control Module PCM i ECT i Sensor 1 Signal i E EE E 49 Instrument Cluster ECT Sensor Signal IP Cluster Engine Coolant Temperature ECT ECT Sensor Sensor Ground pn ees ee Sy Powertrain Control Module PCM Action Taken When the DTC Sets The ECU sets the DTC 15 after 2 consecutive driving cycles with the fault active Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F from the start up coolant temperature and the engine coolant temperature exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used Diagnostic Aids Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure After starting the engine the temperature should rise steadily to about 90 C 194 F then stabilize when the thermostat opens A faulty connection or an 1999 2000 GM
135. tion in the fuel system Check the Manifold Absolute Pressure MAP sensor response and accuracy Check the mixer module assembly for proper installation and leakage Verify proper operation of the regulator control valve Ignition System Checks Note LPG being a gaseous fuel requires higher secondary ignition system voltages for the equivalent gasoline operating conditions If a problem is reported on LPG and not gasoline do not discount the possibility of a LPG only ignition system failure and test the system accordingly Check for the proper ignition voltage output with J 26792 or the equivalent Check for faulty spark plug wires Check for fouled spark plugs Check for an open ignition system ground Refer to Enhanced Ignition System in the GM MD Service Manual Additional Check Check for Service Bulletins Check for manifold vacuum or air induction system leaks Check the generator output voltage Check the EGR valve operation Refer to EGR System Diagnosis in the GM MD Service Manual 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 97 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Backfire DEFINITION The fuel ignites in the intake manifold or in the exhaust system making a loud popping noise Preliminary Check e Referto mportant Preliminary Checks Ignition System Checks Note LPG being a gaseous fuel requires higher secondary ignition system voltages for the equivalent gasoline operating condit
136. to Step 14 Go to Step 11 Go to Step 14 Go to Step 14 Go to Step 13 Go to Step 14 Go to Step 14 B 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 60 Did you find a poor connection 1 Turn OFF the ignition 2 Disconnect the MAF sensor connector 3 Start the engine and allow it to idle 4 Monitor the MAF frequency using a scan tool Does the Scan Tool indicate a MAF sensor frequency 1 Check for a poor connection at the MAF Sensor harness terminals 2 If a poor connection is found replace the faulty terminals Was a poor connection found 1 Perform the following MAF Sensor harness checks for incorrect routing e Near the secondary ignition wires or coils e Near the other high voltage components solenoids relays motors 2 If an incorrect routing is found correct the harness routing Was a problem found Replace the MAF Sensor Is the action complete 1 Check the MAF signal circuit terminal connections at the PCM 2 Ifa poor connection is found repair as necessary Was a poor connection found Replace the ECU Refer to ECU Replacement Is the action complete Replace the PCM Important If the PCM is faulty reprogram the PCM Refer to PCM Replacement Programming The 7 4L LPG fuel system requires a unique PCM software calibration Is the replacement complete Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Sep Adon Vau Yes Op
137. tta te erie a ee eG ee ee Ae ey Powertrain Control Module PCM I ECT 1 Sensor 1 Signal 1 ECT IP Cluster Sem Engine Coolant g Temperature ECT ECT Sensor Sensor Ground Powertrain Sensor Control Module PCM Longer than 600 seconds at intake air temperatures less than 0 C 32 F e ECT circuit voltage is higher than 4 395 Volts Action Taken When the DTC Sets The ECU sets the DTC 14 after 2 consecutive driving cycles with the fault active Conditions for Clearing the MIL DTC The ECU turns the MIL off after 3 consecutive driving trips without a fault condition present A DTC will clear if no fault conditions have been detected for 40 warm up cycles coolant temperature has risen 40 C 72 F from the start up coolant temperature and the engine coolant temperature exceeds 70 C 160 F during that same ignition cycle or the code clearing procedure has been used 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 30 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Diagnostic Aids poor driveability complaints Refer to Temperature vs Resistance Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure Test Description After starting the engine the temperature should rise steadily to about 90 C 194 F then stabilize when The numbers below refer to the step numbers on the the thermostat opens A faulty connection or an diagnostic table op
138. tting this DTC as specified in the supporting text 2 Check to see if the MIL light still illuminates Did the diagnostic run and pass Value s 140 C 284 F Ye mo Go to Step 10 Go to Step 8 140 C 284 F Go to Step 11 Go to Step 12 applicable Go to Step 13 Go to Step 14 Go to Step 13 Go to Step 15 Go to Step 13 Go to Step 15 Go to Step 16 Go to Step 16 Go to Step 17 Go to Step 2 Go to the 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 32 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM Sep Acion O Vae No Go to the Are any ECU or PCM DTCs displayed that have not applicable been diagnosed DTC Table System OK 1999 2000 GM Medium Duty Chassis Service Manual Supplement Page 33 Website 5 29 03 IMPCO PROPANE FUEL SYSTEM DTC 15 ECT Sensor Circuit Low Voltage i Alternative Fuel Se Engine Control 1 Signal Unit AF ECU LI C001 BLU Circuit Description The Engine Coolant Temperature ECT sensor is a thermo resistor that controls the signal voltage to the PCM The PCM applies a voltage on the 5 volt reference circuit to the sensor When the engine is cold the sensor resistance is high therefore the PCM senses a high voltage signal and the PCM indicates a low coolant temperature As the engine warms the sensor resistance becomes less and the voltage drops indicating high coolant temperature At normal engine opera

1999-2000 Medium Duty LPG Service Manual Supplement

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