P0455 — Evaporative Emission Control System Leak Detected (Large Leak)
The EVAP system self-test has detected a large leak (sometimes called a gross leak) in the sealed fuel vapor containment system.
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What the P0455 code means
P0455 means the EVAP system is losing pressure or vacuum far faster than a small-pinhole leak allows — something is notably open, disconnected, or broken.
The classic culprit is a missing or forgotten gas cap, especially right after refueling. Beyond that: a disconnected vapor line, a purge or vent valve stuck open, a cracked hose, or damage from age or repairs in the fuel tank area.
Common symptoms
- Check-engine light, typically appearing soon after a fill-up when the cap was left off or loose
- Occasional strong fuel vapor smell, especially near the rear of the vehicle
- No drivability change in almost all cases
Possible causes
- Missing or loose gas cap (most common)
- Disconnected or cracked EVAP hose
- Purge or vent solenoid stuck open
- Damaged filler neck or tank seal
- A component disturbed during recent fuel-system or rear-suspension work
Diagnostic considerations
Check the timing: a P0455 appearing within a day or two of refueling points strongly at the cap. Retighten it firmly and give the system a few drive cycles to self-test again.
Large leaks are easier to find than small ones — smoke tests or even careful visual inspection often reveals a detached hose. If recent work occurred near the tank, start where hands were last.
What a technician may inspect
- Gas cap present, undamaged, and fully tightened
- EVAP hoses — trace them looking for a disconnect or split
- Purge and vent valve operation
- Filler neck and tank-top components for damage
- Any area of recent service near the fuel tank
Common mistakes
- Clearing the code without ever touching the cap
- Buying a new cap when the hose simply popped off during other work
- Ignoring a persistent vapor smell — it can indicate a fuel leak that deserves immediate attention
When professional inspection is appropriate
Related codes
Related glossary terms
FAQ
Frequently Asked Questions
Can leaving my gas cap off cause P0455?
Yes — it's the textbook cause. Reinstall or tighten the cap and the code often clears on its own after a few drives.
Is a large leak dangerous?
The EVAP leak itself usually isn't, but it vents fuel vapor to the atmosphere and fails inspections. A fuel smell deserves immediate checking to rule out an actual fuel leak.
How long until the light resets itself?
If the cause is fixed, the system typically needs several drive cycles to re-run its self-test. It won't clear instantly with the ignition.
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