P0455 fault code: large leak in the EVAP system
Plain-language definition
EVAP System Leak Detected - Large Leak
What does it mean?
The fuel vapour (EVAP) system stops vapour from the petrol in the tank from escaping into the air. The vapour is first held in a container filled with activated carbon (the canister), then drawn into the engine through the purge valve and burned while the engine is running. That's why the system has to be sealed, from the fuel cap all the way to the hoses.
Under specific conditions, for example when the tank is neither too empty nor too full and the engine temperature is suitable, the engine computer runs a leak test by creating vacuum or pressure in the system and watching whether it holds. If the system can't build up or hold the expected vacuum or pressure, the engine computer reads this as a large leak and stores P0455. The test conditions vary from make to make; some cars run this test after the engine has stopped.
Most of the time you won't feel any change while driving; usually only the check engine light comes on. Sometimes you may notice a smell of petrol around the car, especially on the fuel cap side. A fuel cap that isn't fully closed after filling up is one of the most well-known causes of this code.
How serious is it?
This is a Warning-level code; it usually doesn't affect how the engine runs, but it lets fuel vapour escape into the air. If there's a noticeable smell of petrol, it's a good idea not to delay having it checked, because petrol vapour is flammable.
Severity is a guide; if the warning light is flashing or you notice symptoms while driving, have the car checked at a workshop.
Common general causes
- A fuel cap that isn't fully closed, is loose or has a damaged seal
- Cracked, broken or loosely connected EVAP hoses or lines
- A faulty canister purge valve
- A canister vent valve stuck open
- A cracked or rusted canister or fuel filler neck
- Less often, a faulty pump or pressure sensor used for the leak test
The list shows general causes; a workshop finds the actual cause on your car with a check.
Definitions by make
Some manufacturers record the same code under their own wording:
- Ford
- Evap Emission Control System Leak Detected (Gross Leak/No Flow)
How does it appear in the 2dakika report?
EVAP System Leak Detected - Large Leak
If the code is read as a confirmed (stored) fault, the report shows it with the "Warning" severity; in pending or past records, codes that don't request the warning light and aren't critical appear as "Info". If the engine computer stored them, the conditions when the fault was recorded (engine temperature, rpm, speed) are shown too.
Read this code with the OBD-X1, and clear it from the app after the repair.
Clearing the code doesn't fix the fault; if the problem persists, the code comes back.