P0440 P0xxx · Powertrain (P) Low severity
Evaporative Emission Control System Malfunction
The EVAP system failed its overall integrity check. Fuel vapour is escaping somewhere between the tank and the charcoal canister.
Severity guidance: Low — usually no drivability impact, fix at the next service
Symptoms you will notice
- Fuel smell around the vehicle
- Check-engine light
- Failed emissions test
- Occasional rough idle after refuelling
Common causes
Ordered from most to least likely — start at the top.
- 1 Loose, missing or damaged fuel cap
- 2 Cracked vapour hose
- 3 Failed purge or vent solenoid
- 4 Leaking charcoal canister or tank seal
How to diagnose it
Cheapest and least invasive first — most of these codes are not a parts problem.
- ✓ Check the fuel cap first — it is the single most common cause and costs nothing.
- ✓ Smoke-test the EVAP system at the service port; leaks show up in seconds.
- ✓ Command the purge and vent solenoids with a scan tool and confirm they hold vacuum.
- ✓ Inspect the filler neck and tank seam for rust.
Repair options
- Replace the fuel cap
- Repair the leaking hose or seal
- Replace the vent or purge solenoid
P0440 — frequently asked questions
Is it dangerous to drive? +
Generally not, but a large leak is a fire risk and will fail inspection. Fix it reasonably soon.
Why does it come back after refuelling? +
A cap that does not seal or a damaged filler neck — the system detects the leak right after the tank is opened.
Confirm the diagnosis before you buy parts
Send us the code, freeze-frame data and the vehicle — our engineers will tell you what to test first.