Fault codeP0440

MODERATE

Evaporative Emission Control System Malfunction

What this code means

Evaporative Emission Control System Malfunction.

P0440 is a generic code: it means the same thing on every make. P0440 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 driving symptom. This generic code says the evaporative system did not behave as expected during its self-test, without saying whether it is a leak or a valve that does not respond. It often comes with P0442 or P0455, which narrow it down.

Common causes

Fuel cap loose or worn
Purge or vent solenoid no longer moving
EVAP hose split, pinched or disconnected
Faulty tank pressure sensor
Canister saturated with fuel after repeated brim-filling

How to diagnose it

Note the codes that come with it: they often name the leak or valve concerned. Deal with the cap first, then inspect the accessible hoses.

At idle, the purge solenoid should click and its command be visible on a multimeter or oscilloscope. Without equipment, a workshop smoke test remains the quickest way to conclude.

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

From €10 for a cap to €100 for a solenoid; a pressure sensor costs €40 to €120. Workshop diagnosis: €50 to €100.

How to read this code

PPowertrain
0standardised code
4Emission controls
40P0440