P0457

What it means

P0457 means the control unit has detected a large leak in the evaporative emission (EVAP) system, and the SAE J2012 definition points to a loose or missing fuel filler cap. During the leak test the unit saw the system fail to hold the expected vacuum or pressure, so it set the code. The fault is usually simple, but it can also come from a damaged hose, valve or canister.

Symptoms

• Engine management light on
• Smell of fuel around the car or near the filler area
• Fuel cap warning message on some vehicles
• Difficulty refuelling or the pump clicking off early
• No noticeable change in how the car drives
• Failed emissions test or inspection

Possible causes

• Fuel filler cap loose, missing, cross-threaded or not the correct typelikely
• Worn, cracked or poorly seated fuel cap seallikely
• Damaged or disconnected EVAP hose or pipe, including split or perished rubber connectionspossible
• Purge valve stuck open or leakingpossible
• Vent valve stuck open or faulty, where fittedpossible
• Cracked charcoal canister or damaged filler neckrare
• Corroded or damaged EVAP pipework, particularly underneath the carrare

How to diagnose

1. Read the stored codes and freeze frame data, and note whether the fault appeared after refuelling.
2. Inspect the fuel cap for correct fitting, damage, a worn seal and the right type for the vehicle.
3. Check the filler neck and the sealing surface for damage, dirt or corrosion.
4. Visually inspect accessible EVAP hoses, pipes and connectors for splits, disconnections and perishing.
5. Check the purge valve and vent valve wiring and connectors, and test their operation as per the manufacturer's procedure.
6. Use live data or the manufacturer's service test to see if the purge and vent valves open and close properly.
7. Perform a smoke test of the EVAP system to locate any leak that is not visible.
8. Inspect the charcoal canister and underbody pipes for impact damage or corrosion. The layout depends on the model.

How to fix

• Refit the fuel cap properly, or replace it with the correct type if it is damaged or worn.
• Repair or replace the damaged filler neck or its seal.
• Replace split, perished or disconnected EVAP hoses and pipes, and secure the connectors.
• Replace a faulty purge valve or vent valve.
• Replace a cracked canister or corroded pipework.
• After the repair, clear the code and complete a drive cycle to confirm the EVAP monitor runs and passes.

Can I keep driving?

Nearby codes

• P0456GenericEVAP System Leak Detected (very small leak)
• P0458GenericEVAP System Purge Control Valve A Circuit Low