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Diagnostic Procedure

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. Inspect for applicable service bulletins before proceeding with this test. Ensure both fuel tanks are at least 1/4 full. Do not clear DTCs unless instructed by a diagnostic procedure. Turn the ignition OFF. Connect the scan tool. Turn the ignition ON with the engine OFF. Is the MIL on continuously? If yes, go to next step. If no, see MIL INOPERATIVE  under SYSTEM TESTS.
  2. Using a scan tool, attempt to communicate and retrieve data from the gasoline control module (PCM). If the scan tool fails to turn ON, see SCAN TOOL DOES NOT POWER UP in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. Does the scan tool display gasoline control module data? If yes, go to next step. If no, see SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
  3. Using a scan tool attempt to communicate and retrieve data from the Alternative Fuels ECM. Does the scan tool display alternative fuels data? If yes, go to next step. If no, see IGNITION RELAY DIAGNOSIS under IGNITION SYSTEM in appropriate SYSTEM & COMPONENT TESTING article.
  4. Inspect both control modules for stored DTCs. Record and store the DTC Freeze Frame and Failure Records information using the scan tool if any of the above are set. Were any DTCs stored? If yes, go to step  10 . If no, go to next step.
  5. Command the MIL OFF utilizing the scan tool Engine Output - Gasoline for the MIL. Does the MIL turn OFF? If yes, go to next step. If no, see MIL ALWAYS ON  under SYSTEM TESTS.
  6. Crank the engine for at least ten seconds. Does the engine start? If yes, go to next step. If no, go to step  9 .
  7. Determine which fuel system the engine is operating on by observing the fuel indicator lamp and the scan tool AFO Signal and AFO Signal Command parameters. If the vehicle is operating on GASOLINE and the FIL is NOT illuminated, see FUEL INDICATOR LAMP INOPERATIVE - ALTERNATIVE FUELS in appropriate ANALOG INSTRUMENT PANELS article. If the AFO Signal and the AFO Signal Command parameters do not indicate the same data, see FUEL SYSTEM UNWANTED SWITCH TO GASOLINE (BI-FUEL ONLY) under FUEL SYSTEM (BI-FUEL & CNG) in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER. Is the engine operating on Alternative Fuel? If yes, go to next step. If no, see FUEL SYSTEM UNWANTED SWITCH TO GASOLINE (BI-FUEL ONLY) under FUEL SYSTEM (BI-FUEL & CNG) in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER.
  8. Operate the vehicle and observe/record the engine data parameters. Compare the engine data on the scan tool with the Engine Scan Tool Data List. Are the values normal or within typical range? If yes, go to step  13 . If no, see applicable DTC diagnosis. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  .
  9. Remove the CNG fuse (20-amp). Crank the engine for at least 10 seconds. Install the CNG fuse prior to proceeding to other diagnostic information. Does the engine start and continue to run with the CNG fuse removed? If yes, see IGNITION RELAY DIAGNOSIS (5.7L BI-FUEL) under IGNITION SYSTEM in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER. If no, see ALTERNATIVE FUEL PUMP RELAY under FUEL SYSTEM (BI-FUEL & CNG) in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER.
  10. Does the PCM have a DTC P1665 stored? If yes, go to next step. If no, go to step  12 .
  11. Inspect the PCM for the correct BI-FUEL software and calibration. Is the PCM programmed with BI-FUEL software and calibration? If yes, see FUEL SYSTEM UNWANTED SWITCH TO GASOLINE (BI-FUEL ONLY) under FUEL SYSTEM (BY-FUEL & CNG) in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER. If no, see POWERTRAIN CONTROL MODULE under PROGRAMMING in SELF-DIAGNOSTICS - 5.0L & 5.7L CHEVY EXPRESS & SAVANA.
  12. Compare the stored gasoline control module DTCs to the stored Alternative Fuels ECM DTCs. Diagnose DTCs in the following order: If a DTC is stored ONLY in the gasoline control module, see DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 5.0L & 5.7L CHEVY EXPRESS & SAVANA. If a DTC is stored in BOTH modules or only in the Alternative Fuels ECM, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If DIFFERENT multiple DTCs are set, perform diagnosis on the gasoline control module DTCs first utilizing the gasoline service information. Diagnose DTCs. Have all DTCs been diagnosed? If yes, go to step  17 . If no, see applicable DTC diagnosis.
  13. Is there a driveability symptom? If yes, go to next step. If no, go to step  15 .
  14. Perform the fuel system diagnosis and return to this step. See FUEL SYSTEM DIAGNOSIS (BI-FUEL & CNG) under FUEL SYSTEM (BI-FUEL & CNG) in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER. Did the fuel system diagnosis locate and repair a concern? If yes, go to step  17 . If no, see TROUBLE SHOOTING - NO CODES - TRUCKS article.
  15. Is there a fuel gauge, fuel gauge selector switch or fuel indicator lamp operation concern? If yes, see FUEL GAUGE RELAY DIAGNOSIS - ALTERNATIVE FUELS, FUEL INDICATOR LAMP ALWAYS ON - ALTERNATIVE FUELS, OR FUEL INDICATOR LAMP INOPERATIVE - ALTERNATIVE FUELS in appropriate ANALOG INSTRUMENT PANELS article. If no, go to next step.
  16. With the ignition OFF remove the CNG fuse (20-amp) in order to force a switch-over to gasoline operation. Crank the engine for at least 10 seconds. Does the engine start and run on gasoline? If yes, go to next step. If no, see ALTERNATIVE FUEL PUMP RELAY under FUEL SYSTEM (BI-FUEL & CNG) in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER.
  17. Remove all test equipment except the scan tool. Connect any disconnected components, fuses, etc. Using a scan tool clear DTC information from the Alternative Fuels ECM and the gasoline control module (PCM). Turn the ignition OFF and wait 30 seconds. Start the engine and operate the vehicle. If a DTC was set ensure that the operation of the vehicle allows the DTC to test. Observe the fuel indicator lamp and the MIL. Observe vehicle performance and driveability. After operating the vehicle inspect both control modules for stored DTCs. Does the vehicle operate on CNG with normal driveability, no FIL/MIL illumination and no stored DTCs? If yes, system is okay. If no, go to step  1 .
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