P0440 on a Mazda: Causes, Fixes & Repair Cost

🟢 Low severity · drivable

Safe to keep driving — this is a general emissions-system fault, not a mechanical issue — but fix it before your next emissions test.

What P0440 means on a Mazda

On a Mazda, P0440 means the engine computer detected a general problem in the evaporative emission (EVAP) system that stores fuel vapors from the tank. It is the catch-all EVAP code, less specific than the leak-size codes P0442, P0455, and P0456, so it often appears with other EVAP codes. The car typically drives and performs normally.

Is P0440 common on Mazdas?

P0440 is a common emissions code on Mazdas, frequently starting with a loose gas cap and then, with age, cracked EVAP hoses or a worn purge valve. The small rubber and plastic lines in the EVAP system are the usual leak points. It is an emissions issue, not a drivability issue.

Commonly reported on: Mazda3, Mazda6, CX-5, CX-9.

Symptoms

Check engine light on
Possible faint fuel smell
No drivability symptoms

Common causes

most common: Loose, missing, or failing gas cap
common: Cracked or disconnected EVAP hoses
common: Faulty purge valve
less common: Small leak in the charcoal canister or fuel tank

How to fix it

Fix	DIY?	Typical cost
Tighten or replace the gas cap	Yes	$10–30
Replace cracked EVAP hoses	Yes	$20–80
Smoke test the EVAP system to find the leak	Mechanic	$50–150
Replace the purge valve	Yes	$50–140