The check engine light is on, you read the code, and it says error code P0455. Good news: this is often one of the cheapest codes to fix. It concerns the EVAP system, which captures fuel vapors. In this article, you will read what P0455 means, what the causes are, and how you can usually fix it yourself.
What does error code P0455 mean?
P0455 stands for "Evaporative Emission System Leak Detected (Large Leak)": the system detects a large leak in the EVAP system. That system captures gasoline vapors from the tank and sends them to the engine instead of letting them escape into the air. If the computer sees that the system cannot hold pressure or vacuum, it triggers P0455.
The most well-known cause is almost too simple: a gas cap that is not properly closed. Always check that first.
Symptoms
Check engine light is on. Usually the only symptom. The car drives normally.
Sometimes a gasoline smell. With a real leak, you occasionally smell fuel vapor around the car.
No driving problems. P0455 rarely causes power loss or stalling; it is mainly an emissions code.
Possible causes (from cheap to expensive)
Loose or broken gas cap. By far the most common cause. Tighten it properly or replace it; often the code will then disappear.
Damaged EVAP hose. A torn or loose hose lets vapor escape. Cheap to replace.
Defective purge or vent valve. A valve that does not close properly causes a leak. Slightly more expensive.
Leak in the carbon filter (canister). The catch filter itself can leak. The most expensive but least common cause.
How to determine the cause
Always start with the gas cap: tighten it firmly (until you hear clicks) and clear the code. If P0455 doesn’t return after a few drives, that was it. If the code remains, visually check the EVAP hoses for cracks and loose connections. With a scanner, you can also read if there are related codes for the purge or vent valve, which points you toward the cause.
Which scanner do you use for this?
An affordable scanner is sufficient for reading and clearing P0455:
View the Topdon CarPal → 
View the OBDeleven 3 → 
View the Launch CRP919X →
The Topdon CarPal (around €40) reads and clears the code via your phone. The OBDeleven 3 (around €77) does that plus all modules. The Launch CRP919X (around €440) can often also control the EVAP valves for a test.
Frequently Asked Questions
Can I keep driving with P0455?
Yes, that’s safe. P0455 does not cause driving problems; it’s an emissions code. However, you can fail an emissions test because of it, so fix it in time.
Is it really often the gas cap?
Yes. A loose, dirty, or worn gas cap is the number one cause of P0455. Always check and replace it first before looking further.
Will the light go off by itself?
Sometimes yes. If you tighten the gas cap properly, the light can go off after a few drives. With a scanner, you can clear it immediately.
Can I just clear P0455?
Clearing is possible, but if the leak remains, the code will return. First tighten the gas cap or fix the leak, then clear and check.
In short
P0455 means a large leak in the EVAP system, and the cause is very often simply a loose gas cap. Check that first, then the hoses and valves. Often an inexpensive fix. View the scanners in our diagnostic equipment collection or read how to read and clear fault codes.