Check engine light after refueling: check the fuel cap first

What the warning actually means

Many cars have no dedicated fuel cap light, so a loose cap shows up as the amber check engine light instead.

How the EVAP system works

The evaporative emissions system, EVAP, captures fuel vapor from the tank instead of letting it escape, and the car tests it for leaks. A loose cap is enough to fail that test, and the check engine light comes on.

Common causes

• A fuel cap that is not tightened fully
• A cracked fuel cap
• A missing fuel cap
• A leak somewhere else in the evaporative system

What to do now

1. Check the cap is tightened fully and is not visibly cracked.
2. Drive normally and see whether the light clears after a few drive cycles.
3. Have the code read. A basic scan tool or a free check at most auto parts stores will pull it.
4. Do not clear the code before the cause is fixed.

What people often get wrong

That the light should go out the moment the cap is tightened. Give it a few drive cycles first.

When the car must go to a workshop

If the light does not clear after a few drive cycles with a good cap, the leak may be elsewhere, and the evaporative system should be tested.

Read next

• P0455 and P0442: a leak in the EVAP system
• Your check engine light isn't random
• Flashing check engine light: slow down, this one is urgent

This page is general information and does not replace a professional assessment. Symbols, codes and behaviour vary between makes. Always check the handbook for your own car.