OBD-II diagnostic trouble codes
Every code we've published, in plain English. Each page tells you what the code means, whether you can keep driving, what to check first, and roughly what the repair costs.
21 codes published so far. We add more every week.
No published code matches that yet. We add codes every week — get the free cheat sheet and we'll tell you when new ones go live.
Catalytic converter
Emissions-related codes about how well your exhaust is being cleaned.
Misfires
The engine isn't burning fuel properly in one or more cylinders.
Fuel & air mixture
Too much air or too much fuel reaching the engine.
EVAP system
Fuel-vapour leaks. Often the cheapest codes to fix.
Sensors
Airflow and oxygen sensors that feed data to the engine computer.
EGR system
Exhaust gas recirculation, used to lower combustion temperatures.
Cooling system
Thermostat and coolant temperature codes.
Codes starting with P1 (and P3000–P33FF) are manufacturer-specific. The same code can mean completely different things on a Honda and a Ford, so there's no single correct answer without knowing your make. We only publish verified generic codes. For those, check your manufacturer's service information or use a scanner with enhanced support for your vehicle.
General guidance based on the standard SAE definitions of these codes. A real diagnosis depends on your make, model, year, engine and other symptoms — this is not a substitute for a professional inspection.