P0455 Code: Evaporative Emission Control System Leak Detected (Gross Leak)
The evaporative emissions (EVAP) system, which traps fuel vapors from the tank instead of venting them, has a large leak — the system cannot hold pressure during its self-test.
What this means for driving
P0455 is an emissions-system fault, not an engine or safety fault: it does not affect how the engine runs or how the car handles. The main consequences of leaving it are a failed emissions test and fuel vapor escaping. It is still worth fixing, but it is not the kind of fault that typically requires stopping the car.
When in doubt, have a mechanic assess it promptly. If any of the red-flag symptoms below are present, stop driving and arrange a tow rather than risking it.
Important: This page is general information only — not professional mechanical advice and not a diagnosis for your specific vehicle. Fault causes and severity vary by make, model, year, and condition. A qualified mechanic should confirm any diagnosis before you make driving decisions or authorize repairs.
Red-flag symptoms: stop and get help
- Strong fuel smell inside the car (ventilate and have it checked promptly)
- Visible fuel leak under the vehicle
- Any other warning light appearing alongside it
Symptoms of P0455
- Check-engine light on (often the only symptom)
- Occasional faint fuel smell near the car
- Failed emissions test
Most likely causes, ranked
- Loose, damaged, or missing fuel cap — the single most common cause
- Cracked or disconnected EVAP hose
- Faulty purge or vent solenoid valve stuck open
- Leaking charcoal canister
- Damaged fuel filler neck
How a mechanic diagnoses it
- Fuel cap checked first — tighten it, clear the code, and see if it returns after a few drive cycles.
- If it returns, a smoke test: smoke is pumped into the EVAP system and the leak shows itself visibly.
- Purge and vent valves tested for proper operation.
Likely fixes
- Replace fuel cap (DIY)
- Smoke-test diagnosis
- Replace EVAP hose
- Replace purge or vent valve
- Replace charcoal canister
Repair costs vary by vehicle, region and shop. Get a quote from a local mechanic.
Related codes
- P0442: Evaporative Emission Control System Leak Detected (Small Leak)
- P0171: System Too Lean (Bank 1)
CheckMyCarCode content is general information only and is not a substitute for professional diagnosis. Trouble-code meanings are standardized for generic (P0xxx) codes, but causes, severity, and repairs vary by vehicle. If your car shows a red-flag symptom, stop driving and get professional help.