P0455: Your car found a large leak in the fuel vapor system

Evaporative Emission Control System Leak Detected (Gross/Large Leak)

What it means

Your car captures fuel vapors instead of letting them escape into the air. This sealed system includes the gas cap, fuel tank, vapor hoses, the charcoal canister, and two valves. The computer runs a self-test on it and looks for a leak. P0455 means it found a large one, 0.080 inch (2mm) or bigger. It is an emissions problem, so it almost never changes how the car drives. Here is the trap: the light will not turn off the moment you fix it. The test only re-runs under certain drive and temperature conditions, so it can take several days of driving or a scan tool to clear. Owners see the light the next morning and assume the fix failed.

Common causes

1. Loose, missing, or damaged gas capThe number one cause. Reseat it until it clicks. Check the O-ring seal. Capless systems can have a stuck-open flap.
2. Stuck-open canister vent valveThe most common bad part after the cap, often from water or dust. Common on GM trucks and Nissan/Infiniti.
3. Faulty purge valve or split hose at itStuck open or leaking. Shows up on VW/Audi, Hyundai, and Jeep/Dodge. The usual next suspect after the vent valve.
4. Cracked or disconnected vapor hosesRubber lines rot with age. The big filler-neck-to-tank hose is a known one. A smoke test finds these.
5. Rusted or damaged fuel filler neckA new cap cannot seal a corroded neck lip. Common on older or rust-belt cars.
6. Cracked charcoal canisterLess common and pricier. More likely after road or physical damage to the part.
7. Bad fuel tank pressure sensorLeast common. A misreading sensor can fake a leak that is not there. Test before replacing parts.

What it costs

• Gas cap (do it yourself)$10 to $60
• EVAP smoke test at a shop$50 to $150
• Vapor hose or line repair$50 to $300
• Purge valve replaced$100 to $400
• Vent valve replaced$150 to $500
• Charcoal canister replaced$400 to $620

Symptoms

• Check engine light on, usually the only sign
• Fuel smell near the tank or right after filling up
• Slightly worse gas mileage in some cases
• Failed emissions or smog test
• No change in how the engine runs or drives

What to do next

Check the gas cap first before you buy anything. Reseat it until it clicks, then look at the rubber O-ring and the filler-neck lip for cracks or rust. Do not refuel with the engine running, and do not top off past the click, since both can trigger this code. If the cap is fine, do not start throwing parts at the car. Pay for a $50 to $150 smoke test. Shops replace caps and valves too early, and the leak is often not where you would guess. On GM and Nissan especially, the part found most often is a stuck-open vent valve, which a smoke test or a valve-click test catches in minutes.

Lewis reads this code plus the fuel tank pressure data that shows whether the system is holding a seal, so you can see what a shop would see. Download Lewis.

Related codes

• P0440
• P0441
• P0442
• P0446
• P0456
• P0457

FAQ

Can I drive with a P0455 code?

Yes. It does not hurt the engine and your car drives normally. It also does not threaten the catalytic converter. The two things to watch: if you smell raw fuel near the tank, get it inspected soon, and you will fail an emissions test until it is fixed. Repairing within a few weeks is the safe call.

I replaced the gas cap but the code came back, what next?

Two things. The light may just need time. The system only re-tests under certain drive and temperature conditions, so it can take several days or a scan-tool clear. If the cap truly was not it, pay for a $50 to $150 smoke test before buying parts. The most common bad part is a stuck-open vent valve.

How much does it cost to fix a P0455 code?

A gas cap runs $10 to $60 and you can do it yourself. A smoke test at a shop is $50 to $150. Common part repairs range from about $50 for a hose up to $500 for a vent valve. A charcoal canister is the pricey one at $400 to $620.