P0442: EVAP system leak detected (small leak)
A small leak was found in the fuel vapour (EVAP) system.
Updated
What P0442 means
Petrol gives off vapour. The EVAP system on petrol cars catches it in a charcoal canister and lets the engine burn it, instead of venting it into the air.
To check for leaks, the engine computer seals the system and watches whether the pressure or vacuum holds. The code says how big the leak is. The test only runs under certain conditions, so it can take a while to show up, and to clear.
P0455 and P0456: larger and smaller leaks
The three codes come from the same test. The checks are the same for each, starting with the fuel cap; a very small leak can be the hardest to find.
P0455: EVAP system leak detected (large leak)
A large leak was found in the fuel vapour (EVAP) system.
Common causes: fuel cap missing or loose, disconnected evap hose, faulty purge or vent valve.
P0456: EVAP system leak detected (very small leak)
A very small leak was found in the fuel vapour (EVAP) system.
Common causes: fuel cap seal, small crack in an evap hose, leaking purge valve.
Can I keep driving?
Likely OK to drive
Likely OK to drive for now. Have it fixed before the next emissions inspection (APK, MOT, TÜV, contrôle technique).
General guidance based on the code alone, not on the car’s actual condition. If in doubt, stop and ask a mechanic.
The car drives as before, but fuel vapour escapes, and an emissions inspection that reads OBD sees the code.
Symptoms
- Usually only the check engine light.
- Sometimes a smell of fuel near the car, more likely with a large leak.
Common causes
- Fuel cap not sealing. A worn or damaged seal, or a cap that isn’t closed properly.
- Cracked EVAP hose. Hoses around the tank, the canister and the engine age and crack.
- Faulty purge or vent valve. A valve that doesn’t close lets the system leak during the test.
Typical fixes
- Check the fuel cap: closed properly, and the seal undamaged. Replace it if the seal is worn.
- Look over the EVAP hoses around the fuel tank, the canister and the engine for cracks and loose connections.
- If the leak isn’t visible, a garage can find it with a smoke test.
- Clear the code after the repair. The car has to run its leak test again before the Evaporative system self-test shows as complete, which can take several days of normal driving.
Questions
Can a loose fuel cap turn on the check engine light?
Yes. A fuel cap that isn’t sealing is one of the causes the app lists for EVAP leak codes. Close it properly or replace it, then give the car time to run its leak test again.
Can I drive with P0442?
Likely, for now: the app’s advice is that it’s likely OK to drive, and to have it fixed before the next emissions inspection.
What is the difference between P0442, P0455 and P0456?
The size of the leak the test found: P0455 is a large leak, P0442 a small one and P0456 a very small one. The checks are the same.