Check engine light on?
Say what the code is. We'll show our evidence.
Plain English for owners who are not mechanics. We show where each answer comes from, and we say so when it is not known.
Meanings come from a named, MIT-licensed fault-code dictionary. If safety, causes or costs are not established, we say so instead of guessing. Owner-sourced workshops are listed with their evidence, never paid placement.
Check your car by plate number
Common fault code guides
- P0420
Catalyst System Efficiency Below Threshold Bank 1
- P0430
Catalyst System Efficiency Below Threshold Bank 2
- P0171
System Too Lean Bank 1
- P0174
System Too Lean Bank 2
- 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
- P0011
A Camshaft Position - Timing Over-Advanced or System Performance Bank 1
- P0016
Crankshaft Position - Camshaft Position Correlation Bank 1 Sensor A
- P0128
Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
- P0455
EVAP System Leak Detected - Large Leak
- P0456
EVAP System Leak Detected (very small leak)
- P0442
EVAP System Leak Detected (small leak)
- P0101
Mass or Volume Air Flow Sensor A Circuit Range/Performance
- P0135
O2 Sensor Heater Circuit Bank 1 Sensor 1
- P0401
EGR A Flow Insufficient Detected
- P0507
Idle Control System RPM - Higher Than Expected
- P1086
Manufacturer-specific: BMW, Subaru