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Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Pontiac Sunfire, 2002 Pontiac Grand Am, 2002 Oldsmobile Alero, and 2002 Chevrolet Cavalier. 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. NOTE: Ensure engine speed stabilizes with each commanded RPM change to determine if engine speed stays within 60 RPM of commanded RPM.
  2. Set parking brake and block drive wheels. Install scan tool. Start engine. Turn off all accessories. Use scan tool RPM control function in order to slowly increment engine speed to 1700 RPM, then to 600 RPM, then to 1700 RPM. Exit RPM control function. Does the engine speed stabilize within 60 RPM of the commanded RPM during the test? If yes, go to next step. If no, go to step  4.
  3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running the DTC, and within the parameters observed in the Freeze Frame/Failure Records. Does the DTC fail this ignition? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  4. Turn ignition off. Disconnect IAC valve harness connector. Connect IAC Motor Driver (J-37027-A) to IAC valve. Start engine. Use IAC motor driver to command IAC valve in until 600 RPM is reached. Use IAC motor driver to command IAC valve out until 1700 RPM is reached. Return engine to desired idle speed as indicated on scan tool data list. Did the engine speed steadily decrease to about 600 RPM and steadily increase to about 1700 RPM when the IAC valve was commanded in and out? If yes, go to next step. If no, go to step  11.
  5. Using test light connected to ground, probe one of IAC valve circuits at IAC valve harness connector using Connector Test Adapter Kit (J-35616-A). Start engine. Use IAC motor driver to command low RPM while observing a scan tool until IAC counts start to increment. Using IAC motor driver, command high RPM while observing a scan tool until IAC counts start to increment. While IAC counts are incrementing, observe test light. Return engine to desired idle speed as indicated on scan tool data list. Repeat procedure for other 3 IAC valve circuits. Did the test light remain ON, never flashing, while the IAC counts where incrementing at any of the IAC valve circuits during the test? If yes, go to step  10. If no, go to next step.
  6. Did test light remained off (never flashing) while IAC counts were incrementing at any of IAC valve circuits during the test? If yes, go to step  9. If no, go to next step.
  7. Connect a test light between the IAC coil "A" low circuit and the IAC coil "A" high circuit at the IAC valve harness connector using the J-35616-A Connector Test Adapter Kit. With the J-37027-1A command low RPM while observing a scan tool until the IAC counts start to increment. With the IAC motor driver, command high RPM while observing a scan tool until the IAC counts start to increment. While the IAC counts are incrementing, observe the test light. Return engine idle speed to desired idle as indicated on the scan tool data list. Repeat procedure with the test light connected between the IAC coil "B" low circuit and the IAC coil "B" high circuit at the IAC valve harness connector. Return engine speed to the desired idle as indicated on the scan tool data list. Did the test light stay illuminated and never flashing while the IAC counts where incrementing during the test? If yes, go to next step. If no, go to step  16.
  8. Inspect for a poor connection at the IAC valve harness connector. Did you find and correct the condition? If yes, go to step  17. If no, go to step  12.
  9. Turn ignition off. Disconnect PCM harness connectors. With a DMM, test the circuit where test light remained OFF for an open circuit, short to ground or short to another IAC valve circuit. Did you find and correct the condition? If yes, go to step  17. If no, go to step  12.
  10. Turn ignition on. With a DMM, test the circuit where the test light remained ON for a short to voltage or short to another IAC valve circuit. Did you find and correct the condition? If yes, go to step  17. If no, go to step  12.
  11. Visually/Physically inspect for the following:
    • Throttle body damage and tampering.
    • Throttle lever screw tampering (if equipped).
    • Vacuum leaks.
    • Faulty, incorrectly installed PCV valve and hose (if equipped).
    • Throttle shaft binding.
    • Throttle linkage or cruise control linkage binding (if equipped).

    Remove IAC valve. Inspect for the following:

    • Clogged IAC passage.
    • Excessive deposits on throttle plate.
    • Excessive deposits in throttle bore.
    • Excessive deposits on IAC valve pintle.

    Did you find and correct the condition? If yes, go to step  17. If no, go to step  14.

  12. Inspect for a poor connection at the PCM harness connectors. Did you find and correct the condition? If yes, go to step  17. If no, go to next step.
  13. Disconnect PCM harness connectors. With a DMM, test all IAC valve circuits for high resistance. Did you find and correct the condition? If yes, go to step  17. If no, go to step  16.
  14. Inspect for a poor connection at the IAC valve harness connector. Did you find and correct the condition? If yes, go to step  17. If no, go to next step.
  15. Replace IAC valve. When complete, go to step  17.
  16. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL, OVERHAUL & INSTALLATION article. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE REPROGRAMMING  under PROGRAMMING. After replacing PCM, go to next step.
  17. Use the scan tool in order to clear the DTCs. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  18. With a scan tool, observe the stored information, in Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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