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.

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.

NOTE: Ensure engine speed stabilizes with each commanded RPM change to determine if engine speed stays within 60 RPM for A/T or within 100 RPM for M/T of commanded RPM.

Set parking brake and block drive wheels. Install scan tool. Start engine. Turn off all accessories. Use scan tool RPM control function to slowly increment engine speed to 1700 RPM, then to 600 RPM, then to 1700 RPM. Exit RPM control function. Does engine speed stabilized within 60 RPM for A/T or within 100 RPM for M/T of commanded RPM? If yes, go to next step. If no, go to step 4.
Observe FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within code enable criteria or as close to FREEZE FRAME/FAILURE RECORDS data that you observed. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
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 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.
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.
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.
Connect a test light between IAC coil "A" low circuit and IAC coil "A" high circuit at IAC valve harness connector using the J-35616-A. With J-37027-1A, command low RPM while observing a scan tool until IAC counts start to increment. With 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 test light. Return engine idle speed to desired idle as indicated on scan tool data list. Repeat procedure with test light connected between IAC coil "B" low circuit and IAC coil "B" high circuit at IAC valve harness connector. Return engine speed to the desired idle as indicated on scan tool data list. Did test light stay illuminated and never flashing while IAC counts where incrementing during the test? If yes, go to next step. If no, go to step 16.
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.
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.
Turn ignition on. With a DMM, test the circuit where the test light remained ON for the following: 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.
Visually/Physically inspect for the following:
- Throttle body damage and tampering.
- Throttle lever screw tampering (if equipped).
- Restricted air intake system. Inspect for a possible collapsed or 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. Inspect for the following:
- A 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.
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.
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.
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.
Replace IAC valve. When complete, go to step 17.
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.
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.
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.