P0456EVAP System Leak Detected (very small leak)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. P0456 reports a very small leak of 0.020 in (0.5 mm), as CARB requires. Ford uses the engine-off natural vacuum test: after switch-off the closed system must build at least about 190 Pa pressure or 125 Pa vacuum, judged statistically. Saab's Bosch ME9 also tests with the engine off for up to 45 minutes; VW and Audi use a leak detection pump. GM reports this leak size as P0442 instead. The code often appears only after many trips and depends on the weather.
- What you may notice
- Check engine light on (possibly a check fuel cap message)
- Possibly fuel smell
- EVAP readiness or emission inspection not passed
- Likely causes
- LikelyFuel cap seal worn or cap not clicked in
- PossiblePurge or vent valve not sealing
- PossiblePorous hoses or O-rings, hairline crack in canister or filler neck
- RareLeak detection pump itself leaking (VW/Audi)
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €15 – €450
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.