Number P0457: EVAP System Leak Detected (fuel cap loose/off)
The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. P0457 is a large leak attributed to the fuel cap: Ford detects refuelling and treats a vacuum that is not reach
Can you drive with P0457?
Severity: Plan the repair. Yes — this is an emissions-system fault. The car will generally drive normally, but it will fail an emissions inspection with the light on.
If you ignore it: Fuel economy and emissions creep up, and some faults in this family (rich/lean running) stress the catalyst over time.
This is the #74 most common code in our top-150 library, in the evap — fuel vapor system family (Powertrain system). Severity is Number Nest's editorial triage — if the light is flashing or the car feels unsafe, stop driving it whatever any page says.
What P0457 means
The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. P0457 is a large leak attributed to the fuel cap: Ford detects refuelling and treats a vacuum that is not reached afterwards (about −2 kPa in 30 s) as an open cap. CARB allows a separate check fuel cap lamp instead of the warning lamp, and the code is cleared once the cap is found tight again. Ford sets the lamp after two to three trips depending on calibration, Subaru after two. GM and Saab's ME9 do not use the code.
Systems involved: fuel filler cap, fuel filler neck, evap system.
Causes, ranked by likelihood
| # | Cause | Likelihood |
|---|---|---|
| 1 | Fuel cap not closed, not clicked in or forgotten | most likely |
| 2 | Fuel cap seal faulty or non-original cap | possible |
| 3 | Filler neck sealing surface damaged or capless flap sticking | possible |
| 4 | Vent valve stuck open | less common |
Check them in order — the list is ranked so the likely, cheaper causes come before the expensive part.
Symptoms you may notice
- Check fuel cap lamp or check engine light on
- Fuel smell
- EVAP readiness not set
Misdiagnosis traps
- This is the code the car sets when it is sure the cap is loose or missing — check under the car and in the trunk before paying for diagnosis; spare caps hide everywhere.
- A cap that clicks can still leak at a cracked filler neck — the click tests the ratchet, not the seal.
How a good shop confirms it
- Inspect the cap gasket and the filler neck lip for rust or cracks; smoke-test if a good cap does not hold the fix.
Repair options & costs
| Repair | Shop total (parts + labor) | DIY (parts only) | Difficulty |
|---|---|---|---|
| EVAP leak diagnosis (smoke test) + gas cap | $73 – $248 | $10 – $60 (parts only) | 1/5 |
National ranges from Number Nest's cost model (midsize car, independent shop, US-average labor).
OBDex repair data for this code rates the job difficulty easy with a typical labor time in the 0–0.5 hour range and DIY possible: yes.
Price this repair in your state
Estimated total: — (midsize car, independent shop)
Frequently asked questions
How many clicks for the gas cap?
Until it clicks at least once — the click is a torque limiter. The seal is the rubber gasket against the filler neck; that surface is what to inspect.
How much does it cost to fix P0457?
The fix most associated with this code — evap leak diagnosis (smoke test) + gas cap — runs $73 – $248 at an independent shop for a midsize car in our cost model (parts + labor, US average). The code names a system, not a part, so confirm the cause before spending: the ranked causes above are ordered by likelihood.
Can I drive with P0457?
See the can-you-drive verdict above — it is based on the system involved and the cascading-damage risk, and it is our editorial triage, not a manufacturer instruction. If the light is flashing or the car feels unsafe, stop driving it regardless of any code.
Will P0457 clear itself?
If the fault was a one-off (a loose cap, a cold-start glitch), the light can go out after several clean trips and the code ages into history. A fault that is still present re-sets the code as soon as the car runs that self-test again — monitors run under specific conditions, which is why "it hasn't come back in two days" is not proof of a fix.
Will my car fail inspection with P0457?
In states with OBD-based emissions inspection, yes — an illuminated check-engine light or an incomplete readiness monitor fails the test regardless of what the tailpipe would show. C-codes (ABS) fall under safety inspection instead in states that have one.
What should I check first for P0457?
The first item on the ranked-causes list above — it is ranked likelihood-first for exactly this reason — plus the free checks: recent work in the area (connectors left loose are a classic), fluid levels, and the battery and grounds on electrical codes.
Where this data comes from
Code facts, causes and symptoms come from OBDex — an open dataset of independently authored descriptions of the standardized generic OBD-II codes (CC0 1.0, public domain; github.com/foerbsnavi/OBDex). The SAE J2012 document itself is copyrighted and is not reproduced here. Cost ranges are Number Nest's own US planning model: national parts and labor ranges cross-checked against the CarMD Vehicle Health Index 2026 published averages, with labor adjustable by the BLS OEWS May 2025 state wage index for auto technicians (occupation 49-3023) — a wage index, not a surveyed shop rate. Severity and can-you-drive notes are our editorial triage, not a manufacturer instruction.