P0440 on a GMC: 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 GMC

On a GMC, P0440 means the engine computer found 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 vehicle keeps running and driving normally.

Is P0440 common on GMCs?

P0440 is one of the more common EVAP codes on GMC vehicles, most often starting with a loose gas cap. As the vehicle ages, cracked hoses and a failing purge valve become the usual culprits, especially on trucks with many years of use. It is an emissions issue, not a drivability issue.

Commonly reported on: Sierra, Terrain, Acadia, Yukon.

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 fuel tank or charcoal canister

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