Ignition and misfires OBD codes

This group covers faults in the ignition system and misfires: coils, spark plugs and their circuits, and the sensors the engine computer uses to know the engine's position, such as the crankshaft and camshaft sensors.

The engine computer detects a misfire because the crankshaft speeds up less than expected during that cylinder's stroke. Codes P0301 to P0312 name the specific cylinder, and P0300 indicates random misfires or misfires in several cylinders at once.

A continuous misfire can damage the catalytic converter, because unburnt fuel reaches it. If the check engine light flashes, reduce the load on the engine and have it checked as soon as possible. If the misfire is on one cylinder, swapping its coil or spark plug with another cylinder's and seeing whether the misfire moves is a simple, common check.