A threaded or quarter-turn plastic cap that seals a vehicle's fuel tank. It maintains pressure in the fuel system and prevents hydrocarbon vapors from escaping into the atmosphere. A loose, missing, or defective gas cap is one of the most common causes of an illuminated check engine light, as the evaporative emissions system detects a vacuum leak.
Heard on the job
Read the codes first, half the time an EVAP leak just means the customer forgot to tighten their gas cap.
Also heard as
- fuel cap
- petrol cap