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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. Were you sent here from another diagnostic procedure? If yes, go to next step. If no, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Turn ignition on, with engine off. Is the MIL continuously illuminated? If yes, go to next step. If no, go to MIL INOPERATIVE  .
  3. While communicating with the AF ECM, command the MIL OFF. Is the MIL illuminated? If yes, go to step  5 . If no, go to next step.
  4. The fault is not present. Is an operational concern still present? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, problem is intermittent. See INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  5. Observe the Gasoline MIL Command data parameter in the Alternate Fuels Data List while the MIL is commanded OFF. Is a gasoline MIL Command request present? If yes, go to step  7 . If no, go to next step.
  6. Test the MIL control circuit between the AF ECM connector terminal and IPC for a short to ground. Test the IPC for an internally shorted condition. Repair circuit or IPC as necessary. Was a repair necessary? If yes, go to step  9 . If no, go to step  8 .
  7. Test the MIL INPUT circuit between the AF ECM connector terminal and the PCM connector terminal for a short to ground. Repair the circuit as necessary. Was a circuit repair necessary? If yes, go to step  9 . If no, go to next step.
  8. 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 performing repairs and procedures, go to next step.
  9. Remove all test equipment except the scan tool. Connect any disconnected components, fuses, etc. Using scan tool, clear DTC information from the AF ECM and the Powertrain Control Module (PCM). Turn ignition off and wait 30 seconds. Start engine and operate vehicle. Observe the fuel indicator lamp and the MIL. Observe vehicle performance and driveability. After operating vehicle inspect BOTH control modules for stored DTCs. Does vehicle operate on CNG with normal driveability, no FIL/MIL illumination and no stored DTCs? If yes, system is okay. If no, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
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