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HOMESERVICE MANUALSCHEVROLET2001CAVALIER LS, 2.4 TREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 81 (ENGINE CONTROLS SELF-DIAGNOSTICS - 2.2L BI-FUEL)DIAGNOSTIC TESTSDTC P0148: ALTERNATIVE FUEL ENABLE CONTROL CIRCUITDIAGNOSTIC PROCEDURE
2001 Chevrolet Cavalier LS, 2.4 T

Diagnostic Procedure

2001 Chevrolet Cavalier LS, 2.4 TSECTION 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. NOTE: Verify that there is adequate fuel in the CNG fuel tank before proceeding.
  2. Turn ignition switch to RUN position, engine OFF. Observe the FUEL MODE COMMAND parameter using a scan tool. Does the scan tool display ALT FUEL? If yes, go to next step. If no, go to step  4.
  3. Observe the Freeze Frame and/or the Failure records data 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 SETTING THE DTC . You may also operate the vehicle within the conditions that you observed from the Freeze Frame and/or the Failure records data. Does the DTC fail this ignition cycle? If yes, go to next step. If no, go to INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 2.2L CAVALIER - BI-FUEL - CNG/GASOLINE article.
  4. Command the AF relay ON and OFF using a scan tool. Does the AF relay respond to the scan tool commands? If yes, go to step  10. If no, go to next step.
  5. Turn ignition switch to OFF position. Disconnect the AF relay. Probe the AF relay coil ignition feed circuit using a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step  16.
  6. Probe the AF enable output circuit using a test light connected to battery voltage. Turn ignition switch to RUN position, engine OFF. Command the AF relay ON and OFF using a scan tool. Does the test light turn ON and OFF with each command? If yes, go to step  13. If no, go to next step.
  7. Does the test light remain illuminated with each command? If yes, go to step  9. If no, go to next step.
  8. Check the AF enable output circuit for an open. Did you find and correct the condition? If yes, go to step  20. If no, go to step  14.
  9. Check the AF enable output circuit for a short to ground. Did you find and correct the condition? If yes, go to step  20. If no, go to step  18.
  10. Turn ignition switch to OFF position. Disconnect the AF relay. Probe the AF relay ignition voltage circuit using a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step  16.
  11. Turn ignition switch to OFF position. Install the AF relay. Disconnect the FICM harness connector. Turn ignition switch to RUN position, engine OFF. Probe the AF Enable signal circuit using a test light connected to a good ground. Command the AF relay ON and OFF using a scan tool. Does the test light turn ON and OFF with each command? If yes, go to step  15. If no, go to next step.
  12. Check the AF Enable signal circuit for an open. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  13. Check for an intermittent and for a poor connection at the AF relay. Did you find and correct the condition? If yes, go to step  20. If no, go to step  17.
  14. Check for an intermittent and poor connection at the PCM. Did you find and correct the condition? If yes, go to step  20. If no, go to step  18.
  15. Check for an intermittent and poor connection at the FICM. Did you find and correct the condition? If yes, go to step  20. If no, go to step  19.
    16. NOTE: The AF relay supplies power to the CNG fuel injectors, and the AF injector relays. If the AF relay fuse is open test all circuits for a short to ground.
  16. Repair the ignition voltage circuit of the AF relay for an open or a short to ground. After repair, go to step  20.
  17. Replace the AF relay. After repair, go to step  20.
  18. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION - CAVALIER & SUNFIRE article. Program PCM with correct vehicle software and calibration. After repair, go to next step.
  19. Replace the FICM. After repair, go to next step.
  20. Observe the Freeze Frame/Failure Records for this DTC. 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.
  21. 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.
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.