A code is a clue. Not a verdict.
Decode multiple codes, preserve their relationship, and start a vehicle-aware diagnosis.
A code identifies a monitored condition—not automatically a failed part.
Reviewed code guides
P0300Random or multiple-cylinder misfire detectedEngine · Urgent if the check-engine light flashesP0301Cylinder 1 misfire detectedEngine · Urgent if flashing or running severely roughP0171System too lean — bank 1Fuel & air · Service soon; urgent with misfire or power lossP0420Catalyst system efficiency below threshold — bank 1Emissions · Service soonP0442EVAP system small leak detectedEvaporative emissions · Usually safe to schedule unless fuel odor or liquid leakage is presentP0455EVAP system large leak detectedEvaporative emissions · Schedule promptly; stop for liquid fuel leakageP0128Coolant thermostat temperature below regulating temperatureCooling · Service soon; stop if actual overheating occursP0562System voltage lowElectrical · Urgent if stalling, steering, brake, or multiple system warnings occurP0700Transmission control system requested warning lampTransmission · Depends on shifting behavior; avoid driving if slipping or engagement is unsafeP0135Oxygen sensor heater circuit fault — bank 1 sensor 1Emissions electrical · Service soon