P0457
PowertrainEvaporative Emission Control System (EVAP) Leak Detected
This one is usually a small job, and often free. P0457 means the EVAP system has found a large vapour leak, and on the vast majority of cars the culprit is a fuel cap that wasn't clicked shut properly or has a tired rubber seal. The system is sealed so petrol vapours get burned in the engine rather than venting to the air, and if that seal is broken anywhere the ECU notices. Don't panic and book a big repair before you've checked the cap, because that fixes a huge share of these.
ⓘ Information only. This page provides general educational information about fault code P0457. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0457 mean?
P0457 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Evaporative Emission Control System (EVAP) Leak Detected.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, frequently the only thing you'll notice
- • A whiff of petrol around the back of the car, strongest near the filler flap after refuelling
- • Sometimes a very slight drop in MPG, though many drivers see nothing change
- • Driveability stays normal, no misfire, no limp mode, no loss of power
- • Emissions readiness monitors not completing if you're trying to clear it before an MOT
Possible causes
Causes commonly associated with P0457, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Fuel cap loose, missing, or not clicked home, by far the most common reason and the first thing to rule out
- 2. Perished or split fuel cap seal, the rubber hardens with age and stops sealing properly
- 3. Cracked or disconnected EVAP hoses, these run along the underside of the car and perish or get knocked loose
- 4. Faulty vent or purge valve that won't seal when commanded shut, so the system can't hold pressure
- 5. Split or saturated charcoal canister, common on higher mileage cars, often sits near the rear axle
- 6. Damaged or corroded filler neck where the cap seats, rust here ruins the seal
- 7. Fuel tank pressure sensor reporting wrong, so the ECU thinks there's a leak when the system is actually tight
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Check the fuel cap before anything else. Make sure it's there, that it clicks at least once when you tighten it, and look at the rubber seal for splits, hardening, or grit on the threads. A 5p new cap test saves a lot of bother.
- 2. Scan for other EVAP codes. P0455 (large leak), P0456 (small leak) and P0442 often turn up alongside P0457 and point you toward the same hoses and valves.
- 3. If the cap looks fine, clear the code and drive a few cycles to see whether it comes straight back or stays off.
- 4. Get the car in the air and follow every EVAP hose by eye and hand, checking the charcoal canister and filler neck for cracks, perishing, or a hose that's popped off.
- 5. Run a smoke test through the EVAP system. Most independent garages have a smoke machine and it'll show you exactly where vapour is escaping, including leaks you'd never spot by eye.
- 6. Command the purge and vent valves with a scan tool and confirm they actually hold vacuum when told to close, since a valve stuck open mimics a leak.
Common questions about P0457
Can I carry on driving the car like this? +
Yes, you can drive it normally. P0457 doesn't put the car into limp mode or hurt how it runs, so there's no immediate safety worry. The only real downside is petrol vapour venting where it shouldn't, plus a warning light that'll annoy you. Sort the fuel cap or get it looked at within a week or two rather than ignoring it for months, because a small EVAP fault can grow into a bigger one if a hose is slowly splitting.
Is this going to fail my MOT? +
The code by itself isn't a fail, but the engine warning light is. The MOT checks whether the MIL is illuminated with the engine running, and if it's lit when the tester glances at the dash, that's a fail under the emissions and warning lamp rules. Fix the cause, clear the light, and run a few drive cycles so it stays off before you present it. EVAP faults don't affect the tailpipe gas test on a petrol car, so it's the lamp you're managing, not the readings.
What's it likely to cost to put right? +
If a new fuel cap does it, you're looking at roughly £10 to £30 for a decent OEM-spec one and nothing in labour. A perished hose or a smoke test plus repair at an independent garage tends to land around £60 to £150. A purge valve or vent valve replacement is usually £100 to £250 fitted. A charcoal canister is the pricey end, often £200 to £400 at an independent and more at a main dealer, so it's well worth chasing down the actual leak before anyone fits one.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →