Engine Misfire? Trouble Code P0303 Meaning, Diagnose Spark Plugs & Ignition Coils Do you have a check engine code P0303, which indicates an engine misfire on cylinder 3? In this video, Sue shows you how you can diagnose a misfire without any special tools, just by moving around the spark plug and ignition coil! From there, you can find out whether it is the spark plug or ignition coil that is causing the problem, and replace it yourself! This video focuses on cylinder 3 of a 6 cylinder engine, b