Number P0455: EVAP System Leak Detected - Large Leak
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. P0455 means a large leak or that no vacuum builds up. Ford pulls the closed system down with engine vacuum and
Can you drive with P0455?
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 #23 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 P0455 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. P0455 means a large leak or that no vacuum builds up. Ford pulls the closed system down with engine vacuum and expects about −2 kPa within 30 s; after refuelling it sets P0457 instead. GM sets the code if 20 litres have been purged without reaching 2740 Pa tank vacuum (once per cold start, MIL after two trips). Saab's ME9 uses a pressure drop below 525 Pa. The code also covers blocked purging, for example a purge valve stuck closed.
Systems involved: evap system, fuel filler cap, evap hoses, EVAP purge valve.
Causes, ranked by likelihood
| # | Cause | Likelihood |
|---|---|---|
| 1 | Fuel cap missing, not clicked in or seal faulty (or capless flap) | most likely |
| 2 | Hose off or cracked (canister, filler neck, purge line) | most likely |
| 3 | Vent valve stuck open or purge valve stuck closed | possible |
| 4 | Canister or filler neck cracked or corroded | possible |
Check them in order — the list is ranked so the likely, cheaper causes come before the expensive part.
Symptoms you may notice
- Check engine light on (possibly a check fuel cap message)
- Possibly fuel smell
- EVAP readiness or emission inspection not passed
Misdiagnosis traps
- The classic: a loose or missing gas cap. Check it first — but if the code returns within days, the leak is real and usually at the filler neck or a vent hose.
- A vent valve stuck open reads exactly like a giant leak; the system cannot hold pressure either way.
How a good shop confirms it
- Inspect the cap seal and filler neck, clear the code, and drive several trips.
- If it returns, smoke-test: large leaks show immediately.
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 |
| EVAP purge valve / solenoid | $68 – $198 | $30 – $110 (parts only) | 1/5 |
National ranges from Number Nest's cost model (midsize car, independent shop, US-average labor). Published cross-check — EVAP purge valve / solenoid: CarMD 2026 national average $172.
OBDex repair data for this code rates the job difficulty easy with a typical labor time in the 0.1–3 hour range and DIY possible: yes.
Price this repair in your state
Estimated total: — (midsize car, independent shop)
Frequently asked questions
How fast does P0455 come back if it is a real leak?
The EVAP monitor runs under specific conditions (fuel level between roughly 15% and 85%, cold start) — it may take several drives. A cap fix that holds for a week of normal driving is usually real.
How much does it cost to fix P0455?
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 P0455?
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 P0455 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 P0455?
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 P0455?
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.