P0456
Evaporative Emission System Leak Detected (Very Small Leak)
A very small leak (typically equivalent to a 0.020 inch / 0.5 mm orifice) has been detected. Smaller threshold than P0442; intermittent and often weather-dependent. Modern OBD-II requires this monitor on most vehicles since model year 2000.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
What we see in the workshop
ON FORD ECOBOOST
A very small EVAP leak is most often the fuel cap or its seal. In UAE heat the seals harden early, so we check the cap and filler neck before smoke testing.
Symptoms
- Check engine light on
- Possible smell of fuel near tank or engine bay
- Failed emissions inspection
- Loose-cap warning may appear
Common causes
Ordered by how often each turns out to be the cause.
- Fuel cap seal hardened or wornCommon
- Purge or vent valve leaking slightlyPossible
- Hairline crack in EVAP hosePossible
Parts involved
- Fuel Filler Cap
- EVAP Canister
- EVAP Purge Valve
- EVAP Vent Valve
P0456 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.