OBD2 fault codes explained

What the most common generic fault codes mean, whether you can keep driving, and what usually causes them. The explanations match what Read My Car shows when it reads the code from your car.

These are generic codes: they mean the same on every car. Codes such as P1xxx are manufacturer-specific, and their meaning depends on the make and model.

Catalytic converter

• P0420Catalyst system efficiency below threshold (bank 1)
• P0430Catalyst system efficiency below threshold (bank 2)

Misfires

• P0300Random/multiple cylinder misfire detected
• P0301Cylinder 1 misfire detected
• P0302Cylinder 2 misfire detected
• P0303Cylinder 3 misfire detected
• P0304Cylinder 4 misfire detected

Fuel mixture (lean or rich)

• P0171System too lean (bank 1)
• P0174System too lean (bank 2)
• P0172System too rich (bank 1)
• P0175System too rich (bank 2)

Sensors and idle speed

• P0113Intake air temperature circuit high input
• P0335Crankshaft position sensor "A" circuit malfunction
• P0507Idle control system RPM higher than expected

Engine temperature and oil pressure

• P0128Coolant thermostat (coolant temperature below regulating temperature)
• P0217Engine overheat condition
• P0524Engine oil pressure too low

Turbo, EGR and particulate filter

• P0299Turbo/supercharger underboost
• P0401Exhaust gas recirculation (EGR) flow insufficient
• P2463Diesel particulate filter restriction – soot accumulation

Fuel vapour (EVAP) leaks

• P0455EVAP system leak detected (large leak)
• P0442EVAP system leak detected (small leak)
• P0456EVAP system leak detected (very small leak)

Gearbox, road speed and voltage

• P0700Transmission control system malfunction (see TCM codes)
• P0500Vehicle speed sensor malfunction
• P0562System voltage low

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