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Diagnostic Procedures

WARNING: This page is about a different car, the 2002 GMC Sonoma and 2002 Chevrolet S10 Pickup. 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, 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. Start engine. Turn off all accessories. Using scan tool, select RPM control function and slowly increment engine speed to 1800 RPM, then to 600 RPM, then to 1800 RPM. Exit RPM control function. Does the engine speed stabilize within 60 RPM of the commanded RPM during the above test? If yes, go to next step. If no, go to step  4.
  3. Observe FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within conditions for running this DTC or as close to FREEZE FRAME/FAILURE RECORDS data observed. 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. Using IAC motor driver, command IAC valve in until about 600 RPM is reached, then command IAC valve out until about 1800 RPM is reached. Return engine speed to desired idle as indicated on 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. Using a test light connected to ground, probe one of IAC valve circuits at IAC valve harness connector. Using IAC motor driver, command low RPM while observing scan tool until IAC counts start to increment, then command high RPM while observing a scan tool until IAC counts start to increment. While IAC counts are incrementing, observe the test light. Return engine to desired idle as indicated on scan tool data list. Repeat 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 remained off (never flashing) while IAC counts where 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 and high circuits at 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 procedure with the test light connected between the IAC coil "B" low and high circuits at 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 Digital Multimeter (DMM), test the circuit where the test light remained OFF for the following: 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. Check throttle body for damage and tampering, and throttle lever screw tampering (if equipped). Check for restricted air intake system, collapsed/clogged air intake duct (before and after air filter element), restricted air filter element, or restriction at throttle body intake screen (if equipped). Remove IAC valve. Check for clogged IAC passage, excessive deposits on throttle plate, excessive deposits in throttle bore, or excessive deposits on IAC valve pintle. Repair as necessary. Did you find and correct the condition? If yes, go to step  17. If no, go to step  14.
  12. Check for poor connection at PCM harness connectors. Repair as necessary. 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 IAC valve. After replacing IAC valve, go to step  17.
  16. Replace PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. 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 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 information. 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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