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Diagnostic Procedures

WARNING: This page is about a different car, the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, and 2002 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
  2. Turn ON the ignition, with the engine OFF. Using the scan tool Alternate Fuel Engine Data selection, observe the Alternative Fuels Operation (AFO) Signal and the Alternative Fuels Operation (AFO) Signal Command displays. Do both displays indicate the same information? If yes, go to next step. If no, go to step  10 .
  3. Turn ON the ignition, with the engine OFF. Capture the DTC Information stored when this DTC set from the AF ECM into the scan tool. Clear the DTC information from the AF ECM. Command the Alternative Fuel Operation (AFO) signal circuit back and forth between PCM and AF ECM using the scan tool Alternate Fuels Special Function. Observe the AFO Signal and the AFO Signal Command displays while commanding. Do both displays indicate PCM during one commanded state and then both displays indicate AF ECM during the other commanded state? If yes, go to next step. If no, go to step  11 .
  4. Exit the Special Function area of the scan tool. Start and idle the engine. Observe the Alternative Fuels Operation (AFO) Signal and the Alternative Fuels Operation (AFO) Command displays. Is the engine operating on Alternative Fuel? If yes, go to next step. If no, go to step  8 .
  5. Observe the Idle Control Solenoid (ICS) output circuit status scan tool data parameter while the engine is operating on CNG. Does the data parameter indicate OK? If yes, go to next step. If no, go to step  15 .
  6. Observe the Fuel Control Solenoid (FCS) output circuit status scan tool data parameter while the engine is operating on CNG. Does the data parameter indicate OK? If yes, go to next step. If no, go to step  19 .
  7. Observe the EVAP purge reduce request output circuit status scan tool data parameter during both open loop and closed loop operation. Open loop operation occurs for several seconds after every ignition ON. Closed loop operation occurs after the engine is warm and has been operating for several seconds. Does the data parameter indicate OK? If yes, go to next step. If no, go to step  27 .
  8. Start and idle the engine. Listen for LPL operation as you command the LPL Open and Closed using the scan tool Alternate Fuels Special Function. Does the LPL operate as commanded? If yes, go to next step. If no, go to step  31 .
  9. The fault is not present. See DIAGNOSTIC AIDS  . Are any DTCs stored that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  10. Turn ON the ignition, with the engine OFF. Observe the Alternative Fuels Operation (AFO) Signal display. Does the data parameter indicate the PCM is in control of engine fueling? If yes, go to next step. If no, go to step  12 .
  11. Turn OFF the ignition. Disconnect the AF ECM connectors. Using a fused jumper, connect the AF ECM connector Alternative Fuels Operation (AFO) command circuit terminal to a known-good ground. If the jumper fuse opens, the AFO circuit is shorted to voltage. Turn ON the ignition, with the engine OFF. Using the scan tool, observe the Alternative Fuels Operation (AFO) Signal input data parameter located in the Engine Data - Gasoline list. Does the data parameter indicate the AF ECM is in control of engine fueling? If yes, go to step  14 . If no, go to step  13 .
  12. Turn OFF the ignition. Disconnect the Alternative Fuels ECM connectors. Turn ON the ignition, with the engine OFF. Using the scan tool, observe the Alternative Fuels Operation (AFO) Signal data parameter located in the Engine Data - Gasoline list. Does the data parameter indicate the PCM is in control of engine fueling? If yes, go to step  41 . If no, go to step  14 .
  13. Test the Alternative Fuels Operation (AFO) signal circuit for an open or a high resistance condition. Inspect the PCM connector for proper terminal contact. Repair the wiring or terminals as necessary. Was a wiring or terminal repair necessary? If yes, go to step  43 . If no, go to step  42 .
  14. Test the Alternative Fuels Operation (AFO) signal circuit for a short to ground condition. Repair the wiring as necessary. Was a wiring repair necessary? If yes, go to step  43 . If no, go to step  41 .
  15. Observe the Idle Control Solenoid (ICS) output circuit status scan tool data parameter while the engine is operating on CNG. Does the data parameter indicate OPEN? If yes, go to next step. If no, go to step  23 .
  16. Remove the engine cover. Disconnect the ICS connector. The ICS connector is Red. Jumper the ICS connector terminals together using a fused jumper. Ensure that the engine is operating on CNG. Does the data parameter indicate OPEN? If yes, go to next step. If no, go to step  37 .
  17. Remove the jumper. Connect the Unpowered Test Lamp (J 34142-B) between the ICS ignition relay power circuit terminal "A" and a known-good ground. Ensure that the ignition is ON. Is the test lamp illuminated? If yes, go to next step. If no, go to step  36 .
  18. Test the ICS control circuit for an open condition. Inspect the AF ECM connector terminals for proper contact. Repair the wiring or terminals as necessary. Was a wiring or terminal repair performed? If yes, go to step  43 . If no, go to step  41 .
  19. Observe the Fuel Control Solenoid (FCS) output circuit status scan tool data parameter while the engine is operating on CNG. Does the data parameter indicate OPEN? If yes, go to next step. If no, go to step  25 .
  20. Remove the engine cover. Disconnect the FCS connector. The FCS connector is black. Jumper the FCS connector terminals together using a fused jumper. Ensure that the engine is operating on CNG. Does the data parameter indicate OPEN? If yes, go to next step. If no, go to step  25 .
  21. Remove the jumper. Connect the J 34142-B between the ICS ignition relay power circuit terminal "A" and a known-good ground. Ensure that the ignition is ON. Is the test lamp illuminated? If yes, go to next step. If no, go to step  36 .
  22. Test the FCS control circuit for an open condition. Inspect the AF ECM connector terminals for proper contact. Repair the wiring or terminals as necessary. Was a wiring or terminal repair performed? If yes, go to step  43 . If no, go to step  41 .
  23. Remove the engine cover. Ensure that the engine is operating on CNG. Disconnect the Idle Control Solenoid (ICS) connector. The ICS connector is red. Does the data parameter indicate OPEN? If yes, go to step  37 . If no, go to next step.
  24. Test the control circuit for the shorted condition as indicated by the data parameter. Repair the wiring as necessary. Was a wiring repair performed? If yes, go to step  43 . If no, go to step  41 .
  25. Remove the engine cover. Ensure that the engine is operating on CNG. Disconnect the Fuel Control Solenoid (FCS) connector. The FCS connector is Black. Does the data parameter indicate OPEN? If yes, go to step  38 . If no, go to next step.
  26. Test the control circuit for a shorted condition. Repair the wiring as necessary. Was a wiring repair performed? If yes, go to step  43 . If no, go to step  41 .
  27. Turn the ignition OFF. Disconnect the AF ECM connectors. Turn the ignition ON while with the engine OFF. Connect the DMM test leads between the EVAP canister purge enable control circuit terminal and battery negative. Measure the voltage on the circuit. Is the voltage 4.8-5.2 V? If yes, go to step  40 . If no, go to next step.
  28. Was the voltage greater than 5.2 V? If yes, go to step  30 . If no, go to next step.
  29. Test the EVAP canister purge enable control circuit for an open or shorted to ground condition as indicated by the output data parameter. Inspect the PCM connector terminals for proper contact. Repair the wiring or terminals as necessary. Was a wiring or terminal repair performed? If yes, go to step  43 . If no, go to step  42 .
  30. Test the EVAP canister purge enable control circuit for a short to battery voltage condition. Repair the wiring as necessary. Was a wiring repair performed? If yes, go to step  43 . If no, go to step  42 .
  31. Remove the engine cover. Disconnect the Low Pressure Lock-Off (LPL) solenoid connector. Connect the J 34142-B between the LPL ignition relay power circuit terminal "A" and a known-good ground. Turn the ignition ON, with the engine OFF. Is the test lamp illuminated? If yes, go to next step. If no, go to step  36 .
  32. Connect the J 34142-B between the LPL ignition relay power circuit terminal "A" and the control circuit terminal "B". Start and idle the engine. Observe the test lamp as you command the LPL Open and Closed using the scan tool Alternate Fuels Special Function. Does the test lamp operate as commanded? If yes, go to step  39 . If no, go to next step.
  33. Is the test lamp always illuminated? If yes, go to next step. If no, go to step  35 .
  34. Test the control circuit for a shorted to ground condition. Repair the wiring as necessary. Was a wiring repair performed? If yes, go to step  43 . If no, go to step  41 .
  35. Test the control circuit for an open or shorted to voltage condition. Repair the wiring as necessary. Was a wiring repair performed? If yes, go to step  43 . If no, go to step  40 .
  36. Repair the open ignition voltage supply circuit between the solenoid connector and the ignition relay circuit splice. After repairs, go to step  43 .
  37. Replace the Idle Control Solenoid (ICS). See IDLE CONTROL SOLENOID under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - CHEVY EXPRESS & SAVANA - BI-FUEL. After repairs, go to step  43 .
  38. Replace the Fuel Control Solenoid (FCS). See FUEL CONTROL SOLENOID under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - CHEVY EXPRESS & SAVANA - BI-FUEL. After repairs, go to step  43 .
  39. Replace the Low Pressure Lock-Off (LPL) solenoid. See LOW PRESSURE LOCK-OFF under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - CHEVY EXPRESS & SAVANA - BI-FUEL. After repairs, go to step  43 .
  40. Inspect the AF ECM connectors for proper terminal contact. Repair the terminal contact as necessary. Was a repair necessary? If yes, go to step  43 . If no, go to next step.
  41. Replace AF ECM. See ALTERNATE FUEL ENGINE CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CHEVY EXPRESS & SAVANA - BI-FUEL. Program (flash) AF ECM with correct vehicle software and calibration. See ALTERNATE FUEL ENGINE CONTROL MODULE  under PROGRAMMING. After repairs, go to step  43 .
    42. NOTE: The following Control Module replacement procedures must all be completed before attempting to operate the vehicle.
  42. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CHEVY EXPRESS & SAVANA - GASOLINE. Program (flash) PCM with correct vehicle software and calibration. See POWERTRAIN CONTROL MODULE REPROGRAMMING  under PROGRAMMING. To perform CKP variation learn procedure, a switchover to gasoline operation is necessary. Remove CNG fuse (20-amp) located in underhood fuse block to perform switchover. Perform CKP system variation learn procedure. See CRANKSHAFT POSITION SENSOR SYSTEM VARIATION LEARN PROCEDURE  under PROGRAMMING. After performing repairs and procedures, go to next step.
  43. Using a scan tool, clear the DTC information from both control modules. Operate the vehicle under the Conditions For Running DTC. Using the scan tool parameter DTC STATUS, ensure that this DTC runs. Did this DTC run and pass? If yes, system is okay. If no, go to step  2 .
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