P0446
Evaporative Emission System Vent Control Circuit
What it means
The evaporative emission (EVAP) system traps fuel vapour from the tank in a charcoal canister and later burns it in the engine. The ECU periodically seals the system and checks that it holds pressure or vacuum. The vent valve, which seals the system for leak testing and lets fresh air into the canister, is not working as commanded.
Is it safe to drive?
Safe to drive. The EVAP system only handles fuel vapour, so it does not affect how the car runs, but the car will fail an emissions test and you may smell fuel.
Symptoms
- Check engine light on
- Fuel pump clicking off early or difficulty refuelling in some vehicles
Probable causes
Most likely first
- 1Vent valve stuck or clogged with dirt or spider webs
- 2Failed vent valve coil
- 3Blocked vent filter
- 4Wiring fault
How to diagnose it
Work through these in order before buying parts
- 1Record the code and its freeze frame data (speed, load, temperature when it set), then clear it and see if it comes back.
- 2Locate the vent valve (usually near the canister by the fuel tank) and check it for dirt and debris.
- 3Command the valve with a scan tool and listen for a click.
- 4Check its resistance and wiring.
- 5Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.
Common fixes
- Clean or replace the vent valve
- Replace the vent filter
- Repair wiring
This information is general guidance for all makes. Exact causes, specifications and procedures vary by vehicle, so confirm with your service manual or a qualified mechanic before replacing parts.