P0446 on a GMC: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

Safe to drive, but fix the vent system soon if you notice fuel smells or trouble filling the tank.

What P0446 means on a GMC

On a GMC, P0446 means the vent valve that controls airflow into the EVAP canister is not working correctly — it may be stuck, clogged, or have a wiring fault. When the vent can't open, pressure builds in the fuel tank, which can slow filling. The engine runs normally, so the check engine light is the main symptom.

Is P0446 common on GMCs?

P0446 appears on GMC trucks and SUVs like the Sierra and Yukon as the vent valve near the charcoal canister ages. On trucks the canister and vent valve sit under the frame, where they pick up dirt, moisture, and road salt. A stuck vent valve is the most common cause, with bad wiring and a plugged vent line close behind.

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

Symptoms

Check engine light on
Faint fuel smell near the rear of the vehicle
Slow fuel filling or nozzle clicks off early
No change in how it drives

Common causes

most common: Vent valve stuck closed or failing
common: Faulty vent valve wiring or connector
common: Clogged vent line or canister filter
less common: Damaged charcoal canister

How to fix it

Fix	DIY?	Typical cost
Replace the vent valve	Yes	$60–180
Repair vent valve wiring or connector	Yes	$30–90
Have a shop test the vent circuit and replace the valve	Mechanic	$140–340
Replace the charcoal canister assembly	Mechanic	$280–550