Fuel Caps
The fuel cap seals the filler neck, containing fuel vapour and keeping contamination out. On modern vehicles it forms part of the sealed evaporative emissions system.
What it does
The cap seals against the filler neck and often includes a pressure relief valve. The evaporative system monitors that seal, which is why a loose or perished cap sets a fault code.
Signs a fuel cap is failing
- The engine warning light with an evaporative system fault code
- A fuel smell around the filler area
- A cap that no longer clicks when tightened
- A perished or hardened seal
When to replace them
Not scheduled, but the seal perishes with age and heat. Among the cheapest causes of a warning light.
What to confirm before ordering
Have these ready and the counter can usually confirm the part in under a minute.
- Whether the cap is locking or non-locking
- Thread type and diameter, which vary within a model range
- Whether the vehicle needs a vented or sealed cap
Fuel Caps questions
Can a loose fuel cap trigger the engine warning light?
Yes, and it is one of the most common causes. The evaporative system tests itself for leaks, and a cap that is loose or has a perished seal fails that test and sets a fault code.
Will the warning light clear on its own after tightening the cap?
Often it will, after the system has completed several successful self-tests over a few drive cycles. If it persists, the seal itself has likely failed.