What does my check engine code mean?
Type the code your reader gave you. We will tell you what it means, whether the car is safe to drive, and what usually causes it — not just the dictionary definition.
Codes we see most
Charging
Cooling
Electrical
Emissions
- P0131 O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)
- P0135 O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
- P0141 O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)
- P0401 Exhaust Gas Recirculation Flow Insufficient Detected
- P0420 Catalyst System Efficiency Below Threshold (Bank 1)
- P0430 Catalyst System Efficiency Below Threshold (Bank 2)
- P0440 Evaporative Emission Control System Malfunction
- P0442 Evaporative Emission Control System Leak Detected (Small Leak)
- P0455 Evaporative Emission Control System Leak Detected (Large Leak)
Fuel and air
- P0101 Mass or Volume Air Flow Circuit Range/Performance Problem
- P0113 Intake Air Temperature Circuit High Input
- P0122 Throttle/Pedal Position Sensor A Circuit Low Input
- P0171 System Too Lean (Bank 1)
- P0172 System Too Rich (Bank 1)
- P0174 System Too Lean (Bank 2)
- P0175 System Too Rich (Bank 2)
- P0505 Idle Air Control System Malfunction
Ignition
- P0300 Random/Multiple Cylinder Misfire Detected
- P0301 Cylinder 1 Misfire Detected
- P0302 Cylinder 2 Misfire Detected
- P0303 Cylinder 3 Misfire Detected
- P0304 Cylinder 4 Misfire Detected
- P0305 Cylinder 5 Misfire Detected
- P0306 Cylinder 6 Misfire Detected
- P0325 Knock Sensor 1 Circuit Malfunction (Bank 1)
- P0335 Crankshaft Position Sensor A Circuit Malfunction
- P0340 Camshaft Position Sensor Circuit Malfunction
Timing
- P0011 Camshaft Position - Timing Over-Advanced (Bank 1)
- P0016 Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor A)
Transmission
A code tells you where to look, not what to replace
P0420 does not mean “buy a catalytic converter”. It means the sensors either side of it disagree, and that can be the converter, a sensor, or an exhaust leak upstream. Working out which is the part we do before anything gets quoted.