P0440: EVAP System Malfunction
P0440 means the car's computer found a fault somewhere in the evaporative emission (EVAP) system, which keeps fuel vapor from escaping into the air. It is usually not urgent for the engine, but the check engine light stays on and the car will likely fail an emissions inspection until it is fixed.
You can keep driving
The data lists no limp mode and no change in driving with this code, so the car normally drives as usual. If you smell fuel more than faintly, have it checked soon, and plan the repair so you can pass your emissions inspection.
What it means
The EVAP system collects fuel vapor from the tank in a charcoal canister. A purge valve then lets the engine draw that vapor off and burn it, and a vent valve opens the canister to fresh air. P0440 is the general code for a problem in this system, without saying whether the cause is a leak, a purge flow problem or a failed part. Most manufacturers now use more specific codes instead, such as P0441, P0455, P0456 or P0457, so P0440 is not set the same way on every car. It shows up in VW code lists, and in one FCA bulletin for an Alfa Romeo 2.0 engine it was fixed with a software update. Emission rules require the car to monitor both purge flow and leaks, which is why the light comes on.
Likely causes
- Fuel cap leaking, loose or wrongVery likely
The cap seals the tank, so a loose, worn or incorrect cap lets vapor escape and the system sees a fault.
- Purge valve leaking or stickingPossible
If the valve does not open and close properly, vapor flow to the engine is wrong or the system cannot hold a seal.
- Leaking or cracked EVAP hoses, canister or vent valvePossible
Cracks or a stuck vent valve let vapor out or keep the system from sealing and flowing correctly.
- Engine module softwareLess likely
On some cars the code is set incorrectly, and an update to the engine computer's software corrects it.
What you may notice
- Check engine light on
- Possibly a slight fuel smell
- Readiness or emissions inspection not passed
- No change in how the car drives
What to check, cheapest first
- 1Check the fuel cap: make sure it is present, fits your car, is not cracked, and clicks tight. Replace it if it looks worn or is the wrong type. · you can do it
- 2Clear the code after tightening or replacing the cap and drive normally for several days. A drive cycle (a set pattern of driving that lets the computer re-run its self-tests) is needed before the system tests again. · you can do it
- 3Look at the EVAP hoses you can see near the tank, canister and engine for cracks, loose ends or damage. · you can do it
- 4Read the stored code and any related codes (P0441, P0442, P0455, P0456, P0457, P0443) to narrow down the fault. · mechanic
- 5Test the purge valve and the vent valve to see whether they open, close and seal properly. · mechanic
- 6Run a leak test of the EVAP system and check whether a software update for the engine module exists for your car. · mechanic
Related codes
Frequently asked questions
Can I keep driving with a P0440 code?+
Usually yes. The data shows no limp mode and no change in driving. Get it repaired so the light goes off and you can pass inspection.
Can a gas cap cause P0440?+
Yes. A leaking, loose or wrong fuel cap is the most likely cause, so check it first.
Will P0440 pass an emissions test?+
Probably not. The code is emissions related and the light is on, and the car may also not have completed its readiness checks. Fix the cause and complete a drive cycle before the test.
Can I fix it myself?+
Often, in part. Checking or replacing the cap and looking over hoses is easy. Valve and leak testing is medium difficulty, and the listed repair time ranges from about 0.2 to 2.5 hours.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10