The petrol cap is a threaded or quarter-turn closure that seals the fuel tank filler neck. Caps incorporate pressure-relief and vacuum valves and are a major component of the evaporative emissions system. A loose or damaged cap will fail to hold tank pressure, which triggers a vacuum leak code and illuminates the check engine light.
Heard on the job
The customer came in with an EVAP code, but it turned out they just didn't click the petrol cap tight after filling up.
Also heard as
- gas cap
- fuel cap