What P0440 means
The EVAP system captures fuel vapour from the tank and burns it in the engine instead of venting it. P0440 is the family's general code: the system failed its self-test somewhere — often a leak, sometimes a component — without the computer narrowing it further.
What you’ll notice
- Check engine light and nothing else
- Occasionally fuel smell near the car
- Emissions test failure
Likely causes and repair cost
Broad US independent-shop bands, parts and labour.
Can you drive with P0440?
Completely — EVAP faults are environmental, not mechanical. The car neither knows nor cares; the emissions station does.
The misdiagnosis to avoid
Paying for diagnosis before trying the cap. Remove it, inspect the seal for cracks, refit until it clicks, drive normally for a few days — the light self-clears if that was it. It frequently was. Every EVAP code on this site starts with the same free move.
Describe what it’s doing in your own words and the symptom checker gives you a safe-to-drive verdict, ranked causes with costs, and notes to take to the shop — free, no sign-up.
Read the code yourself
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Check price on AmazonQuestions people ask
How does a gas cap turn on a warning light?
The EVAP self-test pulls a small vacuum on the sealed tank system and watches for decay — an unsealed cap fails the test identically to a cracked hose. The system can't see what leaked, only that vacuum didn't hold, so the humble cap and a $500 canister produce the same light.
The light went off by itself. Fixed?
If you reseated the cap — yes, genuinely: the system re-ran its test on later drives, passed, and cleared its own code. If you changed nothing, the leak may be intermittent (temperature-dependent seals do this) and the light will likely revisit. Either way, note it for context if it returns.