P0455 — EVAP system large leak detected
The evaporative emissions system (gas-tank vapor control) saw a large leak — often a loose gas cap, but not always.
What it means in plain English
P0455 means the EVAP monitor detected a large leak in the vapor recovery system. The classic first check is the gas cap. Larger faults include purge/vent valves, cracked hoses, or a damaged charcoal canister. It rarely means “your engine is dying.”
Common causes
- Loose, damaged, or missing gas cap
- Failed purge or vent valve
- Cracked EVAP hose or canister
- Filler-neck seal problems
What you can safely check
- Click the gas cap until it ratchets; inspect the rubber seal for cracks.
- After a proper cap, it may take several drive cycles for the monitor to pass — don’t expect an instant light-off.
- Avoid “guaranteed EVAP in a bottle” as your only plan.
Pull the code yourself (disclosed)
BlueDriver is a BlueDriver/Levanta affiliate link. We may earn from qualifying purchases. See our affiliate disclosure. Shop directory listings are never affiliate links.
A reusable Bluetooth OBD-II scanner lets you read the code and freeze-frame data before authorizing “mystery” diagnostics. One option: BlueDriver Bluetooth Pro OBD-II scan tool (BlueDriver/Levanta affiliate). Any capable OBD-II reader is fine — this is not required to use Fair Auto Shops.
When to go to a shop
If a known-good cap doesn’t clear it after drive cycles, shops use smoke machines to find hose/canister leaks. Ask for that test before authorizing a canister.
Typical related repair costs (U.S. national averages)
These are related repairs shops may find after diagnosis — not a guaranteed bill for every P0455. Ranges exclude taxes, fees, diagnostics, and your location.
- $138–$150 national average for gas cap replacement (RepairPal; estimates last updated September 3, 2026; excludes taxes/fees and location; source). Labor $24–$36; parts about $114.
- $210–$251 national average for purge valve replacement (RepairPal; estimates last updated September 3, 2026; excludes taxes/fees and location; source). Labor $65–$95; parts $146–$156.
Start with the cap when the seal looks bad. Canister replacement can cost more than these parts — demand smoke-test confirmation.
Related cost guides: Gas Cap · Purge Valve
Questions to ask before you authorize work
Use questions before you authorize a repair and how to read a repair estimate. Watch for patterns in spotting upselling.
Find an honest independent shop
Greater LA · NYC · Chicago · Houston · Phoenix · Seattle · Denver · Dallas · Atlanta · DC
Shop listings are never affiliate links.
FAQ
Will a new gas cap always fix P0455?
Often yes if the cap was the leak — not always. If the light returns, the leak is elsewhere in the EVAP system.
More check-engine codes
P0420 · P0430 · P0300 · P0301 · P0171 · P0174 · P0456 · P0442 · P0446 · P0128 · P0401 · P0133 · P0113 · P0506 · P0507 · P0700 · P0741 · P0011 · P0325 · P0340 · P0335 · P0101 · P0299 · P0135 · P0440 · P0441 · P0010 · P0500 · P0121
Hub: How to read a check-engine code · Repair cost guides · Affiliate disclosure