Check Engine Light (MIL)
Caution — Service soon
What It Means
The Malfunction Indicator Lamp means your vehicle's ECU has detected a fault in the engine, emissions, or fuel system. This is the most common warning light, covering everything from a loose gas cap to a failed catalytic converter.
Common Causes
- Loose or damaged gas cap (most common — tighten first)
- Faulty oxygen sensor (upstream or downstream)
- Worn spark plugs or ignition coils
- Failing catalytic converter (often secondary to other issues)
- Mass airflow (MAF) sensor failure
- EVAP system leak (small or large)
- EGR valve stuck open or closed
Can I Still Drive?
Steady light: usually safe to drive short distances, but diagnose soon. Flashing light: STOP immediately — active engine misfire can destroy the catalytic converter within minutes. Tow to a shop if flashing.
Estimated Repair Cost
$0 – $3,000
This is an estimate only. Actual costs vary by vehicle make, model, year, location, and shop labor rates. Always get multiple quotes for major repairs.
Related OBD-II Trouble Codes
These OBD codes are commonly associated with this warning light. Scan your vehicle with an OBD-II scanner to get the exact code before diagnosing.