OBD-II Code P0455 — What It Means & How to Fix It

What Does This Error Mean?

P0455 means a large leak has been detected in your EVAP (Evaporative Emission Control) system. The EVAP system captures fuel vapors from the gas tank to prevent pollution. A large leak means a significant amount of vapor is escaping. Despite the word large, this code is often caused by something very simple — like a missing gas cap. You will not notice any driving problems, but the check engine light will stay on.

Affected Models

All vehicles 1996+
Very common in Jeep Grand Cherokee and Wrangler
Common in Dodge Ram and Durango
Common in Ford F-150
Common in Toyota Tundra and Tacoma

Common Causes

Gas cap is missing, loose, or the rubber seal is cracked
EVAP canister vent valve is stuck open
Large crack or disconnection in an EVAP hose under the vehicle
Fuel tank filler neck is cracked or rusted through
EVAP canister purge valve is stuck in the open position

How to Fix It

Check the gas cap first. Make sure it is present, not cracked, and the rubber seal is intact. Tighten it until it clicks. If the seal is damaged, replace the cap.

A missing or very loose gas cap causes the majority of P0455 codes. A new cap costs $10 to $20.
Look under the vehicle near the fuel tank for any obvious disconnected hoses. EVAP hoses are usually small-diameter rubber or plastic lines running from the tank area forward.

Road debris can knock hoses loose. A disconnected hose is a large leak that will trigger P0455.
Inspect the EVAP canister vent valve. It is usually located near the charcoal canister under the vehicle or near the rear of the car. Make sure its electrical connector is plugged in.

The vent valve should be open when unpowered and closed when powered. Test it by applying 12 volts briefly.
Check the fuel filler neck where the gas pump nozzle goes in. Look for rust holes, cracks, or a deteriorated rubber seal. This is especially common on older vehicles in cold climates.

Road salt accelerates rust on filler necks. Shine a flashlight to look for rust-through holes.
Clear the code and drive for several days. If it returns and you cannot find the leak visually, take it to a shop for smoke testing.

Smoke testing pumps visible smoke through the entire EVAP system. The smoke escaping shows exactly where the leak is.

When to Call a Professional

If the gas cap checks out, EVAP leak diagnosis requires a smoke machine. Most home mechanics do not own one, so a shop visit makes sense. Smoke testing costs $50 to $100 and pinpoints the leak quickly. Repairs are usually affordable — $50 to $300 for most EVAP components. Fuel filler neck replacement is pricier at $200 to $500 on some vehicles.

Frequently Asked Questions

What is the difference between P0442 and P0455?

P0442 means a small leak was found in the EVAP system. P0455 means a large leak was found. Large leaks are often easier to find because they are more obvious. Ironically, P0455 is often the simpler fix — it is more likely to be a missing gas cap.

Can I pass emissions with P0455?

No, any active check engine light is an automatic emissions test failure. P0455 is specifically an emissions-related code. You need to fix the leak and clear the code before your emissions test. After repair, drive for several days so the EVAP system readiness monitor completes.

Is it safe to drive with P0455?

Yes, P0455 does not affect engine performance or safety. The only issue is that fuel vapors are escaping into the atmosphere. Your fuel economy may decrease very slightly. The main reason to fix it is to pass emissions and clear the check engine light.