Diagnostic Aids

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.

Check for the following conditions:

Incorrect CKP System Variation data stored in the PCM. Run the CKP System Variation Learn Procedure using the scan tool. See CRANKSHAFT POSITION SENSOR SYSTEM VARIATION LEARN PROCEDURE under PROGRAMMING.
The system grounds. Ensure all connections are clean and properly tightened.
A damaged accessory drive belt or driven accessory. A damaged serpentine belt or belt driven accessory can cause engine load variations sufficient to set a misfire DTC.
The fuel pressure. Perform a fuel system pressure test. A malfunctioning fuel pump, a plugged filter, or a malfunctioning fuel system pressure regulator will contribute to a lean condition. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
The fuel injectors. Refer to Fuel Injector Coil Test. See FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
Contaminated fuel.
An extended Idle. Excessive Open Loop operation caused by extended idling or short trip driving may leave deposits on the heated oxygen sensors (HO2S). The deposits cause oxygen sensors to respond slowly to exhaust oxygen content, affecting fuel control and causing a misfire to be indicated at idle. This condition is not permanent. In order to determine if this condition is causing the DTC P0300 to be set, review the Freeze Frame/Failure Records for DTC P0300. If the DTC P0300 occurs at high engine speeds, the condition described above did not cause the DTC P0300 to set. If the DTC P0300 occurs at idle or very low engine speeds and at engine coolant temperatures below 176°F (80°C), the condition described above is very likely the cause of the DTC P0300 being set. The deposits on the heated oxygen sensors can be eliminated by operating the vehicle fully warm at mass air flows above 15 g/s.
Running the vehicle low on fuel. This DTC may set if the vehicle misfires while running out of fuel. If no misfire is currently present, but the History Counters indicate random misfire was once present, ask if the vehicle has been run out of fuel. If this is the case, no further repair may be necessary.

NOTE: If the level of misfire was sufficient to cause possible catalyst damage, and if the MIL was flashing, ensure that the DTC P0420 test is completed and passed after verifying the misfire repair. See DTC P0420: CATALYST SYSTEM LOW EFFICIENCY .

If the condition is intermittent, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM.