P0442 EVAP System Leak Detected (small leak)

Not urgent

The ECU has logged a fault on P0442. 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

P0442: EVAP System Leak Detected (small leak).

P0442 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

Your car stores petrol vapour from the fuel tank in a charcoal canister and feeds it into the engine to be burnt rather than letting it escape. Every so often the engine management seals that system off and checks whether it holds. P0442 means it didn't hold, by a small margin - the ECU has decided there's a leak somewhere between a pinhole and a small crack in size. Nothing about how the car drives will change, but the engine light will be on, and on an OBD-equipped car an illuminated engine light is an MOT failure in its own right.

Most likely causes, in order

Fuel filler cap or its seal. By far the cheapest and one of the most common causes. The rubber seal hardens and flattens with age and heat, or the cap simply hasn't been turned until it clicks. Take it off, look at the seal for cracking or a permanent flat spot, refit it properly and drive the car for several days before deciding it's something else.
Perished or cracked vapour pipework. The lines running between the tank, the charcoal canister and the engine include plastic sections and push-fit connectors, and on many VAG cars parts of that run sit under the car exposed to salt and stones. Age makes the plastic brittle so it splits at bends and joints. Look for chafed, cracked or disturbed pipework around the canister and along the tank.
Purge valve not sealing fully. The purge valve (N80 in VAG documentation) should shut completely when it isn't being commanded open. If its seat weeps, the sealed test slowly bleeds away through the inlet manifold and reads as a small leak. Sometimes a slightly uneven idle goes with it, but often there's no symptom at all beyond the light.
Tank flange seal, canister vent valve or leak detection pump. The large seal where the fuel pump/sender unit fits into the top of the tank, and the vent valve on the canister, both perish on higher-mileage cars. Many older VAG petrol models also carry a leak detection pump on or beside the canister, and its internal rubber diaphragm can split - the pump is part of the sealed system, so when it leaks the ECU sees exactly this. None of these can be judged by eye from outside, which is where a smoke test earns its money.

Worth knowing: Have the system smoke-tested before buying anything beyond a filler cap. Small-leak codes are found in minutes with smoke and cost a fortune in guessed parts otherwise. Also be aware the leak test only runs under particular conditions, so after any repair it can take several drives for the light to either stay off or come back - don't assume the first part cured it.

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.

$249 once. No subscription, unlimited cars. Windows 10/11.

See VAGPULSE — $249 Look up another code

Software downloads instantly · cable ships September 30 · cable guarantee — refund if it won't connect

Prefer to work on your phone? The VAGPULSE Android app is a free download and its demo mode runs against a sample car with no hardware at all, so you can see exactly what it reads before spending anything. Reading your car with it needs the VAGPULSE cable, which comes with the licence.

Common questions

What does P0442 mean?

P0442 means EVAP System Leak Detected (small leak). It is logged when the ECU sees this circuit outside its expected operating window.

Can I drive with P0442?

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.