Diagnostic Aids

WARNING: This page is about a different car, the 2004 GMC Envoy XUV, 2004 GMC Envoy XL, 2004 Chevrolet TrailBlazer, and 2004 Buick Rainier. However, it is still accessible from the selected car via links, so may be relevant.

Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration:
- Thickness variation of the brake rotors-Refer to Symptoms - Hydraulic Brakes in Hydraulic Brakes.
- The drive shaft not balanced-Refer to Vibration Analysis - Driveline in Vibration Diagnosis and Correction.
- Worn or damaged accessory drive belt-Refer to Symptoms - Engine Mechanical in Engine Mechanical-4.8L, 5.3L and 6.0L
There may be more or less cylinders actually misfiring than indicated by the scan tool.
Spray water on the secondary ignition components using a spray bottle. Look and listen for arcing or misfiring.
If there are multiple misfires on only one bank, inspect the fuel injector and ignition coil, power and ground circuits for that bank. Refer to Engine Controls Schematics .