P0456: Evaporative Emission System Leak Detected (Very Small Leak)
P0456 means Evaporative Emission System Leak Detected (Very Small Leak). The EVAP system traps fuel vapour from the tank and burns it in the engine. The engine computer seals the system and checks whether it holds pressure or vacuum. This code means a very small leak was found, typically equivalent to a hole of about 0.5 mm (0.020 in). These are the hardest leaks to find; a smoke test is the best method.
Can I keep driving? Safe to drive short-term, but have it checked to avoid failed emissions or worse fuel economy.
Common symptoms
- Check engine light on
- Usually no drivability change
- Possible fuel smell
Possible causes
- Loose, damaged or wrong fuel cap
- Cracked or disconnected EVAP hoses
- Leaking purge valve or vent valve
- Cracked charcoal canister
- Rusted or damaged filler neck
How to diagnose P0456
- Check the fuel cap seal and that it clicks tight. Clear the code and see whether it returns.
- Smoke-test the EVAP system to find the leak.
- Command the purge and vent valves with a scan tool and check that they seal.
- Inspect the filler neck and canister.
Small EVAP leaks can take several drive cycles to set and to clear. After fixing, the monitor needs to run again before the light stays off.
What the code means, digit by digit
Generic codes have the same definition on every OBD-II vehicle (petrol cars from model year 1996 in the US, 2001 in the EU; diesels later). Manufacturers can add their own enhanced codes; those are not listed here.
Symptoms linked to P0456
Related codes
General guidance only. Fault codes describe what the engine computer saw, not which part failed: confirm with testing before replacing parts, and follow the vehicle's service information.