P0455 EVAP System Leak Detected (Large Leak)

Not urgent

The ECU has logged a fault on P0455. The definition below is the exact wording the standard uses for this code.

Can you drive it? This is an emissions/EVAP fault. It will not hurt the engine and the car drives normally, but it will fail an emissions test and keeps the light on.

The definition

P0455: EVAP System Leak Detected (Large Leak).

P0455 is a powertrain code (the engine or gearbox), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.

What to check first

Cheapest and fastest checks first:

Read the freeze-frame data stored with the fault - engine speed, load and temperature at the moment it logged tell you whether this happens cold, hot or under load.
Check the connector at the part for corrosion, and that it is fully seated.
Clear the code and see whether it returns, and under what conditions.

What actually causes this on a VAG

This is the same evaporative emission leak test as P0442, but failed by a wide margin - the sealed system lost pressure or vacuum straight away, as though something is plainly open. On VAG cars that's most often the fuel filler cap, then a pipe that's off, split or crushed, a cracked canister, or a valve stuck open. You may notice a petrol smell around the car after a drive or after filling up.

Most likely causes, in order

Filler cap not fitted or not sealing. Very often this code appears within a day or two of refuelling. The cap may not have been turned until it clicked, it may be a cheap aftermarket one that doesn't seal properly, or its rubber may have hardened. Refit it correctly, clear the code and give it several days of normal driving.
A vapour pipe off, split or crushed. Look for a disconnected pipe at the charcoal canister or at the purge valve on the engine, and for lines crushed by a jack or trapped by a badly refitted undertray. The section near the canister takes road damage and goes brittle with age.
Cracked canister, vent valve stuck open, or a split leak detection pump. The canister body can crack and its vent valve can be damaged or held open by corrosion, which is more common on cars that spend winters on salted roads. Many older VAG petrol models also have a leak detection pump mounted on or beside the canister, and a split diaphragm inside it leaks straight into the test. All are confirmed once someone can get the car up and put smoke through the system.
Purge valve held open. A valve stuck open leaves the whole system permanently connected to the inlet, which the leak test reads as a large leak. It often brings a rough idle with it, particularly cold or just after a fill-up.

Worth knowing: Do the free thing first - take the cap off, check the seal, refit it until it clicks, and drive the car for a few days. A large share of P0455s are exactly that. If you can smell fuel strongly, or you find damp pipework near the tank, get it looked at promptly rather than living with it: that's vapour escaping, not just a number failing a test.

Reading the code is the easy part

A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.

VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.

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Common questions

What does P0455 mean?

P0455 means EVAP System Leak Detected (Large Leak). It is logged when the ECU sees this circuit outside its expected operating window.

Can I drive with P0455?

This is an emissions/EVAP fault. It will not hurt the engine and the car drives normally, but it will fail an emissions test and keeps the light on.