P0303 Fault in 2006 Saturn Ion 2.2L Automatic: Causes and Diagnosis
I own a 2006 Saturn Ion with a 2.2L engine and automatic transmission. The vehicle is showing a P0303 diagnostic trouble code, indicating a misfire in cylinder 3. I've already replaced the spark plugs at 114,000 miles, and this is a one-owner vehicle with all maintenance records intact. Previously, I worked at a Saturn dealership, so I have firsthand experience with these vehicles. The only noticeable symptom is that the engine sounds louder than usual. The check engine light has come on and stayed on for about a week before turning off, then reappearing intermittently. Given that spark plug replacement was performed, what could be causing this misfire? Are there any other components I should inspect? Thank you, Cathy Fisse
It's important to confirm whether OEM spark plugs were used—avoiding aftermarket brands like Bosch. For a misfire in cylinder 3, the diagnostic process should follow this order: check spark presence, inspect the plug condition using a scope or visual read, verify injector pulse signal, and assess compression levels.