Emission codes
P0455: evaporative emission system large leak
P0455 is the most common reason for a check engine light just after a fill-up. The computer tried to seal the fuel vapor system and found it wide open.
P0455: can I drive, and what will the labor cost?
Estimated labor, replace the gas cap
$11 to $22
| Labor time (estimate) | 0.1 to 0.2 h |
| Rate used | $110/h |
| Technician wage, United States (average) | $27.13/h |
| Low: fix when convenient Safe to drive; check the gas cap first, which is the most frequent cause. | |
Labor only: parts and the diagnostic fee are not included. Hours are our estimate for a typical car; book times vary by model. Wage: BLS, May 2025.
P0455 is the generic OBD-II code for "evaporative emission system leak detected, large leak". When the computer runs its vapor system test, it expects to build a measurable vacuum or pressure in the sealed tank and canister. With P0455, little or none forms, as if a large opening were present. The classic cause is the gas cap left off, loose or not clicked shut after refueling, and the first thing to do is check it. A purge valve stuck closed, so that the test cannot pull a vacuum at all, can look the same to the computer. A hose that has come off the canister or the filler neck, and a cracked filler neck or canister, are the less frequent causes. It is safe to drive, and there is no reason to stop. Tighten or replace the cap and drive normally: if the cap was the cause, the light goes off by itself after 3 trips in which the test passes.
After the repair: when does the light go off?
Light off by itself after about
2 days
| Fault-free trips needed | 3 |
| Warm-up cycles before the code can be erased | 40 |
| Stored code gone after about | 40 days |
Federal rule for model years up to 2016 (40 CFR 86.1806-05); a misfire or fuel fault must also stay away under similar conditions. Clearing codes with a scanner also resets the readiness monitors an inspection checks.
Codes, rules and labor data checked by Radif Partners · Editorial policy · Method and sources
P0455 at a glance
| Code | P0455 |
| Standard description | Evaporative Emission System Leak Detected (Large Leak) |
| System | Evaporative emissions (EVAP) |
| Severity | Low: fix when convenient |
| Common symptoms | fuel smell, gas cap warning message on some cars |
Why the light takes days to go off
The EVAP test does not run every time you drive. Most systems run it only after the car has sat long enough for the fuel to cool, with the tank between about a quarter and three quarters full, and within a range of outside temperatures. It may take several days before the test runs and passes, and the light needs 3 consecutive trips without the fault (40 CFR 86.1806-05). The counter on this page turns that into days for your driving.
If the cap was not it
- Look under the hood and along the frame for a vapor hose that has come off its fitting; a recent repair nearby is a good place to start.
- A purge valve that does not open prevents the vacuum test; a shop can command it with a scanner.
- A cracked filler neck, rusted where it meets the body, is common on older vehicles in salt states.
- A smoke test finds what the eye cannot.
How it differs from the cap code
Some cars have a dedicated code, P0457, that the computer sets when it sees a leak right after refueling, which it interprets as a cap problem. P0455 makes no such assumption. Smaller leaks set P0442 or P0456, which take more effort to find.
Likely causes of P0455, in order
| Cause | How often |
|---|---|
| Gas cap left off or not tightened | most frequent |
| Purge valve stuck closed | frequent |
| Disconnected vapor hose | frequent |
| Cracked filler neck or canister | less frequent |
P0455 repairs and labor time
| Repair | Labor (estimate) | At $110/h |
|---|---|---|
| Replace the gas cap | 0.1 to 0.2 h | $11 to $22 |
| EVAP smoke test to find the leak | 0.5 to 1 h | $55 to $110 |
| Replace the fuel filler neck | 1 to 2.5 h | $110 to $275 |