Check Engine Light
The engine control unit has found a fault in the engine, ignition, fuel or emission system and stored a fault code.
High risk
If the light is steady, the car is usually safe to drive to a workshop soon. If it flashes, the engine is misfiring: reduce speed and avoid hard acceleration.
Short answer · Can I drive with the check engine light on?
Usually yes, if the light is steady and the car drives normally: book a diagnosis soon. If it flashes, the engine is misfiring and unburnt fuel can overheat the catalytic converter, so slow down and drive only as far as you need to. First read the stored fault code.
What to do
- Notice how it behavesSteady and flashing mean different things. Note when it came on and anything else you noticed, such as rough running or a smell.
- Check the fuel capA loose or damaged fuel filler cap is a common cause of evaporative-system codes. Close it until it clicks; the light may need several drives to go out.
- Read the fault codeAny OBD-II scanner reads the stored code in a minute. The code tells you which system set the light; open its page on PitClue for the meaning and causes.
- Book a diagnosisA code points to a system, not always to a part. A workshop confirms the cause with measurements before replacing anything.
How is the light behaving?
| What you see | What it usually means | What to do |
|---|---|---|
| Steady | A fault was stored in the engine or emission system | Drive normally and have it diagnosed soon |
| Flashing | Active misfire that can damage the catalytic converter | Reduce speed, avoid hard acceleration, get it checked now |
| On for a few seconds at start-up | Normal bulb check | Nothing |
Possible causes
- Loose or faulty fuel capThe evaporative system detects a leak and stores a code.
- Ignition misfireWorn spark plugs, ignition coils or injectors cause misfire codes.
- Oxygen or air-flow sensor faultThe engine cannot measure the mixture correctly.
- Catalytic converter efficiencyThe converter no longer cleans the exhaust as it should.
- Vacuum or intake leakUnmetered air makes the mixture lean.
Don't confuse it with
Questions about Check Engine Light
Will the check engine light reset by itself?
Yes, if the fault is no longer detected over several drive cycles, the engine control unit switches the light off. The code stays in memory for a while.
Is it safe to clear the code with a scanner?
Clearing it hides the warning but does not fix the cause. Note the code first; if the fault returns, the light comes back.
Can a check engine light fail an inspection?
In many countries a lit malfunction indicator fails the emissions part of a roadworthiness test.
Why does the light flash?
Flashing means misfiring is strong enough to damage the catalytic converter. Drive gently and have it checked straight away.