Diagnostic Aids
WARNING: This page is about a different car, the 2003 GMC Sierra and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The misfire index counts the number of misfires. The scan tool can monitor the misfire index. There is a current misfire counter and a history misfire counter for each cylinder. Use the current misfire counter in order to determine which cylinder is misfiring. Use the history misfire counter for misfires that are not currently present.
Many different conditions can cause an intermittent misfire. Inspect the following conditions:
- Inspect the Ignition Control (IC) circuit for an intermittent short to ground.
- Ensure that the spark plug wires are securely attached to the spark plugs and the ignition coil.
- If the misfire occurs when the weather is damp, the condition could be due to worn spark plug wires.
- Test or inspect for contaminated fuel or a fuel filter restriction. A restricted fuel filter can cause a misfire.
- Inspect for sticking intake or exhaust valves.
- Inspect the Heated Oxygen Sensor (HO2S) for abnormal voltage readings.
- Inspect for a vacuum leak as a possible cause of the engine misfire.