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Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Pontiac Grand Am, 2002 Oldsmobile Alero, 2002 Chevrolet Monte Carlo, and 2002 Chevrolet Impala. 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 that engine speed stabilizes with each commanded RPM change to determine if engine speed stays within 150 RPM of the commanded RPM.
  2. Set the parking brake and block the drive wheels. Install a scan tool. Start the engine. Turn OFF all accessories. With the scan tool RPM control function slowly increment engine speed to 1700 RPM, then to 600 RPM, then to 1700 RPM. Exit the RPM control function. Does the engine speed stabilize within 150 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 the engine. Operate the vehicle within the Conditions for Running the DTC and within the parameters observed in the Freeze Frame/Failure Records. See CONDITIONS FOR RUNNING DTC . Does the DTC fail this ignition? If yes, go to next step. If no, go to DIAGNOSTIC AIDS .
  4. Turn ignition off. Disconnect the IAC valve. Connect an J-37027-1A IAC Motor Driver to the IAC valve. Start the engine. With the J-37027-1A, command the IAC valve in until near 600 RPM is reached. With the J-37027-1A, command the IAC valve out until near 1700 RPM is reached. Return engine speed to desired idle as indicated on the scan tool data list. Did the engine speed steadily decrease to near 600 RPM and steadily increase to near 1700 RPM when the IAC valve was commanded in and out? If yes, go to next step. If no, go to step  11.
  5. With a test light connected to ground, probe one of the IAC valve circuits at the IAC valve harness connector using the J-35616-A Connector Test Adaptor Kit. Start the engine. With the J-37027-1A, command low RPM while observing a scan tool until the IAC counts start to increment. With the J-37027-1A, 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 this procedure for the 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 the test light remain OFF, never flashing, while the IAC counts where incrementing at any of the 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 IAC coil "A" high circuit at the IAC valve harness connector using the J-35616-A. With the J-37027-1A, command low RPM while observing a scan tool until the IAC counts start to increment. With the J-37027-1A, 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 this procedure with the test light connected between the IAC coil "B" low circuit and 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 the PCM harness connectors. With a DMM, test the circuit where the 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 ON the ignition. 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. Inspect for throttle body damage and tampering, throttle lever screw tampering (if equipped), vacuum leaks, faulty or incorrectly installed PCV valve and hose (if equipped), throttle shaft binding, throttle linkage or cruise control linkage binding (if equipped). Remove IAC valve and inspect for debris in IAC passage, excessive deposits on throttle plate, throttle bore or on IAC valve pintle. Repair any of the conditions as necessary. 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 the 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 the IAC valve. After repairs, go to step  17
  16. Replace PCM. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE  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 the 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. Using scan tool, observe stored information and 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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