Diagnostic Aids

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 Pontiac Grand Prix, 2003 Pontiac Bonneville, 2003 Chevrolet Monte Carlo, 2003 Chevrolet Impala, and 2003 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.

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

Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources
1. Variable thickness brake rotors.
2. Worn or damage accessory drive belt. See ENGINE MECHANICAL in TROUBLE SHOOTING - BASIC PROCEDURES article in GENERAL INFORMATION.
Spray water on the secondary ignition components using spray bottle. Look and lister for arcing or misfiring.