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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 351 (Engine Controls Self-Diagnostics - 2.2L Bi-Fuel) >> Diagnostic Tests >> DTC P1021-P1024: CNG Injector Control Circuit >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2003 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check - Engine Controls (Alternative Fuels). If yes, go to next step. If no, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS (ALTERNATIVE FUELS)  under SELF-DIAGNOSTIC SYSTEM.
  2. Turn ignition switch to OFF position for 30 seconds. Start and idle the engine. Observe the DTC information using a scan tool. Do any of the DTCs P1021-P1024 fail this ignition cycle? If yes, go to step  4. If no, go to next step.
  3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING THE DTC . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, go to DIAGNOSTIC AIDS .
  4. Turn ignition switch to OFF position. Disconnect the suspect CNG injector harness connector. Turn ignition switch to RUN position, engine OFF. Probe the CNG fuel injector Ignition 1 voltage circuit using a test light that is connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step  11.
    5. NOTE: The test light will blink until the vehicle switches over to gasoline.
  5. Probe the CNG fuel injector control circuit using a test light connected to battery voltage. Start the engine. Does the test light blink? If yes, go to step  9. If no, go to next step.
  6. Does the test light remain illuminated? If yes, go to step  8. If no, go to next step.
  7. Check the CNG fuel injector control circuit for an open or a short to voltage. Did you find and correct the condition? If yes, go to step  14. If no, go to step  10.
  8. Check the CNG fuel injector control circuit for a short to ground. Did you find and correct the condition? If yes, go to step  14. If no, go to step  13.
  9. Check for an intermittent and for a poor connection at the CNG fuel injector. Did you find and correct the condition? If yes, go to step  14. If no, go to step  12.
  10. Check for an intermittent and for a poor connection at the FICM. Did you find and correct the condition? If yes, go to step  14. If no, go to step  13.
  11. Repair the open or short to ground in the fuel injector ignition 1 voltage circuit. After repair, go to step  14.
  12. Replace the CNG fuel injector. After repair, go to step  14.
  13. Replace the FICM. After repair, go to step  14.
  14. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Turn ignition switch to RUN position, engine OFF. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING THE DTC . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step  2. If no, go to next step.
  15. Observe the CAPTURE INFO using a scan tool. Are there any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay at this time.
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