Check engine light on
The check engine light means the engine computer has stored a fault code. The code is the starting point: it tells you which system to look at.
AreaEngine
UrgencyModerate
Can I keep driving? Drivable with care. Diagnose soon: performance, economy or other components can be affected.
Common causes
Loose fuel cap
Sets EVAP leak codes; tighten and wait a few drive cycles.
Oxygen sensor or catalytic converter
Very common on older cars.
Misfire
A flashing light means a severe misfire: reduce load.
MAF sensor or vacuum leak
Fuel trim codes.
EVAP system
Small leaks, purge valve faults.
What to check
- Read the code with an OBD2 scanner (inexpensive, or free at many parts stores).
- Look up the code in our OBD2 database.
- A flashing light means stop hard driving now.
Related OBD2 codes
- P0420 Catalyst System Efficiency Below Threshold (Bank 1)
- P0300 Random/Multiple Cylinder Misfire Detected
- P0171 System Too Lean (Bank 1)
- P0442 Evaporative Emission System Leak Detected (Small Leak)
- P0455 Evaporative Emission System Leak Detected (Large Leak)
- P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
Repair guides
Other engine problems
General guidance only. A qualified technician can confirm the cause; brakes, steering and fuel leaks should be checked professionally if in doubt.