Fault codeP0442

MODERATE

Evaporative Emission Control System leak Detected (small leak)

What this code means

A small leak is letting fuel vapour escape. The most common cause is a loose fuel cap or a worn seal.

P0442 is a generic code: it means the same thing on every make. P0442 belongs to family P04xx — Emission controls. Its page explains how to read a code and groups all its codes by part.

Fuel vapour recovery (EVAP)

The EVAP system traps fuel vapour from the tank in a charcoal canister, then burns it in the engine through a purge valve. A vent valve and a pressure sensor let the control unit test the system for leaks, often after the car has been parked.

Symptoms

No symptom at the wheel, never a breakdown: the evaporative system only exists to hold the fuel vapour from the tank. The control unit put the system under vacuum and found it did not hold. A smell of petrol near the parked car is the only possible clue.

Common causes

Fuel cap loose, missing or with a worn seal — by far the most common cause
Split or disconnected EVAP hose
Canister purge or vent solenoid not closing fully
Cracked canister
Leaking filler neck or fuel sender gasket

How to diagnose it

Start with the cap: tighten it until it clicks, or replace it if its seal is cracked. Clear the code and drive for several days — the leak test only reruns under certain fuel level and temperature conditions, and the code can take a while to go.

If the code returns, the leak is elsewhere: inspect the hoses around the canister and the tank. The reliable diagnosis is done in a workshop with a smoke machine, which makes the leak visible in minutes.

Watch it live in Klaro

With an OBD2 adapter plugged in, these live readings show the part at work, when your car reports them:

Commanded evaporative purge
Evap system vapor pressure
Fuel level

What to do

Have it checked this week. The car remains usable, but the fault will not clear itself and will fail the roadworthiness test.

Clearing a code switches the light off but repairs nothing: if the fault remains, the code comes back. Clearing a fault code yourself →

Repair cost

A fuel cap: €10 to €30. A hose: a few euros. A purge solenoid: €30 to €100. A smoke test in a workshop: around €50 to €100.

How to read this code

PPowertrain
0standardised code
4Emission controls
42P0442