Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. 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, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM.

NOTE: Incorrect CKP system variation data in the PCM may cause DTC P0300 to set with no apparent misfire. Any of the following conditions can cause incorrect CKP system variation data:

Replacing the engine.
Replacing the PCM.
Reprogramming the PCM.
Replacing the CKP sensor.
Performing internal engine repairs that affect the CKP sensor to crankshaft reluctor wheel relationship.

If any of the above conditions apply to this vehicle, the CKP System Variation Learn Procedure must be performed before proceeding with misfire diagnosis. See CRANKSHAFT POSITION SENSOR under PROGRAMMING.

Are any other DTCs set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
Start the engine. Select the Misfire Bar Graph on the scan tool. The Misfire Current counters can also be used. Do any cylinders indicate an excessive amount of misfire? If yes, go to next step. If no, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM.
Does the misfire appear to be affecting specific cylinders? If yes, go to step 8 . If on, go to next step.
Inspect the following system grounds:
- PCM grounds.
- Ignition control module grounds.
Ensure that the grounds are clean, tight, and in their proper locations. If a condition is found, repair as necessary. Did you find and correct the condition? If yes, go to step 13 . If no, go to next step.
Test the fuel pressure. See appropriate BASIC DIAGNOSTIC PROCEDURES article. If a fuel system pressure condition is found, repair as necessary. Did you find and correct the condition? If yes, go to step 13 . If no, go to next step.
Test for excessive water, alcohol, or other contaminants. If a condition is found, repair as necessary. Did you find and correct the condition? If yes, go to step 13 . If no, go to next step.
Inspect the following areas for vacuum leaks:
- Vacuum leaks between the intake manifold and the cylinder head.
- Injector O-rings.
If a condition is found, repair as necessary. Did you find and correct the condition? If yes, go to step 13 . If no, go to next step.
Test for proper fuel injector operation. See appropriate SYSTEM & COMPONENT TESTING article. If a condition is found, repair as necessary. Did you find and correct the condition? If yes, go to step 13 . If no, go to next step.
Test for proper ignition system operation. If a condition is found, repair as necessary. Did you find and correct the condition? If yes, go to step 13 . If no, go to next step.
Inspect and/or test for the following mechanical problems:
- A damaged accessory drive belt or pulley.
- A damaged driven accessory, such as a generator, a water pump, a drive belt a tensioner, etc.
- A loose or broken motor mount.
- A base engine mechanical problem.
If a condition is found, repair as necessary. Did you find and correct the condition? If yes, go to step 13 . If no, go to next step.
Test for proper transaxle TCC operation. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS. If a condition is found, repair as necessary. Did you find and correct the condition? If yes, go to next step. If no, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM.
Clear the DTCs with a scan tool. 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 .
Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.