Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.

Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM.

NOTE: Ensure engine speed stabilizes with each commanded RPM change to determine if engine speed stays within 100 RPM of the commanded RPM.

Set parking brake and block drive wheels. Start engine. Turn all accessories off. Using scan tool RPM control function, slowly increment engine speed to 1700 RPM, then to 600 RPM, then back to 1700 RPM. Exit RPM control function. Does the engine speed stabilize within 100 RPM of the commanded RPM during the test? If yes, go to next step. If no, go step 4.
Using scan tool, observe FREEZE FRAME and/or FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within Conditions for Running DTC or as close to FREEZE FRAME and/or FAILURE RECORDS data as possible. Does the DTC fail this ignition? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
Turn ignition off. Disconnect IAC valve 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 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 a test lamp connected to ground, probe any IAC valve circuit at IAC valve harness connector using Connector Test Adapter Kit (J-36616). Start engine. 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. Observe test lamp while IAC counts are incrementing. Return engine idle speed to desired idle as indicated on scan tool data list. Repeat procedure for remaining 3 IAC valve circuits. Did the test lamp remain ON, never flashing, while the IAC counts were incrementing at any of the IAC valve circuits during the above test? If yes, go to step 10. If no, go to next step.
Did the test lamp remain off (never flashing) while IAC counts were 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 lamp between the IAC coil "A" low circuit and 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 the 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 IAC counts are incrementing, observe the test lamp. Return engine idle speed to desired idle as indicated on scan tool data list. Repeat procedure with test lamp connected between the IAC coil "B" low circuit and high circuit at IAC valve harness connector. Return engine speed to desired idle as indicated on scan tool data list. Did test lamp 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.
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 connectors. PCM is located in engine compartment, inside air filter housing. Using a DVOM, check for an open or short ground on IAC valve circuit where test lamp remained off. Did you find and correct the condition? If yes, go to step 17. If no, go to step 12.
Turn ignition on. Using a DVOM, check for short to voltage on IAC valve circuit where test lamp remained illuminated. Did you find and correct the condition? If yes, go to step 17. If no, go to step 12.
Visually and 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.
Check for poor connections at PCM 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. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step 17.
Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE under PROGRAMMING. After repairs, go to next step.
Use the scan tool in order to clear the DTCs. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the 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, 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.