P0446 on a Mercedes-Benz: 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 Mercedes-Benz

On a Mercedes-Benz, P0446 means the vent valve that controls airflow into the EVAP canister is not working as it should — it may be stuck, clogged, or have a wiring fault. When the vent can't open, pressure builds in the fuel tank. The engine runs smoothly, so the check engine light is the main symptom.

Is P0446 common on Mercedes-Benzs?

P0446 appears on Mercedes models like the C-Class, E-Class, and GLE as the vent valve near the charcoal canister ages. The valve can stick from dirt or fail electrically, and its lines under the car can get clogged. It is an emissions fault, not a sign of engine trouble.

Commonly reported on: C-Class, E-Class, GLC, GLE.

Symptoms

Check engine light on
Faint fuel smell near the rear of the car
Slow fuel filling or nozzle clicks off early
No change in how the car 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	$80–220
Repair vent valve wiring or connector	Yes	$40–110
Have a shop test the vent circuit and replace the valve	Mechanic	$160–400
Replace the charcoal canister assembly	Mechanic	$320–680