Fuel filler cap loose, missing, cracked or with a worn seal; Perished or cracked EVAP hoses, loose pipe connections or damaged quick-release fittings; Purge valve sticking partly open or leaking internally; Vent valve or leak detection pump faulty or not sealing (design varies by model); Charcoal canister cracked or leaking at its connections; Corroded or damaged filler neck or EVAP pipes, particularly underneath the car; Fuel tank pressure sensor giving a drifting or inaccurate reading.

P0456

EVAP System Leak Detected (very small leak).

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
4: AreaAuxiliary emission controls
56: FaultThe specific fault in that area

What it means

P0456 means the evaporative emission (EVAP) control system has failed its leak test and the control unit has found a very small leak, roughly equivalent to a hole of about 0.5 mm. The engine control unit seals the system and applies vacuum or pressure, then checks that it holds. If the pressure change or decay rate exceeds the limit during the test, the code is set.

Symptoms

Engine warning light on
Fuel smell around the car, especially after parking
Usually no change in driving or performance
Fuel filler cap warning message on some cars
Failed emissions or MOT test

Possible causes

Fuel filler cap loose, missing, cracked or with a worn seallikely
Perished or cracked EVAP hoses, loose pipe connections or damaged quick-release fittingslikely
Purge valve sticking partly open or leaking internallylikely
Vent valve or leak detection pump faulty or not sealing (design varies by model)possible
Charcoal canister cracked or leaking at its connectionspossible
Corroded or damaged filler neck or EVAP pipes, particularly underneath the carpossible
Fuel tank pressure sensor giving a drifting or inaccurate readingrare

How to diagnose

Read the stored and pending codes and the freeze frame data, noting fuel level, temperature and whether any other EVAP codes are present.
Check the fuel filler cap for correct fit, a damaged seal and cracks, and make sure it clicks or tightens properly.
Visually inspect accessible EVAP hoses, connectors and the filler neck for splits, perishing, loose fittings or corrosion.
Check the purge valve and vent valve electrical connectors and wiring for damage, then test the valves' operation and sealing using the manufacturer's procedure.
Inspect the charcoal canister and its pipework for cracks, damage or signs of fuel contamination.
Check the fuel tank pressure sensor signal against the expected values with the system at rest.
Carry out a smoke test of the EVAP system at the correct low pressure to pinpoint the small leak.
Clear the code after repair and run the system's monitor, following the drive cycle for the specific vehicle, to confirm it passes.

How to fix

Replace or properly refit the fuel filler cap if it is damaged, worn or not sealing.
Replace perished or cracked EVAP hoses and refit or replace damaged connectors and clips.
Replace a purge valve or vent valve that leaks or sticks.
Replace a leaking charcoal canister or a damaged filler neck or EVAP pipe.
Replace a faulty tank pressure sensor or leak detection pump after confirming the fault by testing.

Can I keep driving?

Low severity

The car is safe to drive and this normally does not affect how it runs. Book it in for repair soon, because it will fail an emissions test and may allow fuel vapour to escape.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.