OBD2 code P0420 means your catalytic converter system isn’t working efficiently enough. Learn what P0420 really means, common causes, how to diagnose it at home, when you actually need a new catalytic converter, and how to avoid wasting money on guesswork repairs.

Learn what OBD2 code P0300 (random/multiple cylinder misfire) really means, the most common causes, how to diagnose it at home with a basic scan tool, and the repairs needed to protect your engine and catalytic converter.

OBD2 readiness monitors tell you if your car’s self-diagnostic tests have completed. If they’re “not ready,” you can fail emissions, chase false codes, or waste time on parts. Learn what each monitor does, why it won’t set to ready, and how to fix readiness issues the right way.