P0442 on a GMC: Causes, Fixes & Repair Cost

🟢 Low severity · drivable

Safe to keep driving — this is an emissions leak, not a mechanical issue — but fix it before your next emissions test.

What P0442 means on a GMC

On a GMC, P0442 means the engine computer found a small leak in the evaporative emission (EVAP) system that stores fuel vapors from the tank. GMC trucks and SUVs monitor fuel tank pressure closely, so a small leak in a hose, cap, or valve sets the code. The vehicle keeps running and driving normally.

Is P0442 common on GMCs?

P0442 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