What happens if the vent valve is stuck closed?

The gas tank cannot breathe. On some vehicles this creates enough vacuum to partially collapse the tank. You may hear creaking from the tank or have difficulty refueling.

Is P0446 the same as a gas cap problem?

No. The vent valve is a different component from the gas cap. A loose cap sets P0455 or P0457. P0446 is specifically about the vent circuit.

How hard is this to fix at home?

Moderate. The vent valve is usually accessible, but it may be under the car near the fuel tank. The part is cheap and the electrical test is straightforward.

Codes › P0446

P0446: The EVAP vent valve has a circuit fault

Evaporative Emission Control System Vent Control Circuit Malfunction

Low severityCan you keep driving?

Yes. This will not affect how the car drives. The EVAP system will not seal properly for self-testing, and you will fail emissions, but it is not a safety issue.

What it means

The EVAP vent valve sits on the charcoal canister and normally stays open, venting the canister to fresh air. When the computer runs the EVAP pressure test, it closes this valve to seal the system and checks whether pressure holds. P0446 means the computer detected a problem with the vent valve circuit specifically. A key detail: the vent valve is normally open and only closes during testing. If it fails open, the system cannot seal for the self-test. If it fails closed, the fuel tank cannot breathe normally, which can collapse the tank on some vehicles.

Common causes

Faulty EVAP vent valve solenoidThe solenoid fails electrically. Most common failure on Toyota and GM vehicles.
Wiring or connector fault at the vent valveThe vent valve is near the charcoal canister, often in a wheel well or under the vehicle, exposed to road debris.
Clogged vent valve from contaminationMud or debris from the road can block the vent valve on vehicles where it is undercarriage-mounted.
Faulty vent valve filterSome canisters have a filter at the vent; if it is clogged, airflow is restricted.

What it costs

EVAP vent valve replacement$50 to $200
Wiring or connector repair$60 to $200

Symptoms

Check engine light on
No change in driving feel
Possible fuel smell
Fuel filler door difficult to open or fueling is noisy (tank breathing issue)
Failed emissions test

What to do next

Locate the charcoal canister, usually near the fuel tank or in a wheel well. Inspect the vent valve and its connector for damage or corrosion. Test the solenoid resistance with a multimeter. On many Toyotas and Lexus vehicles, this is a well-known failure point; the vent valve is a common, inexpensive fix.

Lewis shows both the purge and vent valve commanded states during the EVAP monitor cycle so you can see which side of the system is failing to respond. Download Lewis.

Related codes

FAQ

What happens if the vent valve is stuck closed?: The gas tank cannot breathe. On some vehicles this creates enough vacuum to partially collapse the tank. You may hear creaking from the tank or have difficulty refueling.
Is P0446 the same as a gas cap problem?: No. The vent valve is a different component from the gas cap. A loose cap sets P0455 or P0457. P0446 is specifically about the vent circuit.
How hard is this to fix at home?: Moderate. The vent valve is usually accessible, but it may be under the car near the fuel tank. The part is cheap and the electrical test is straightforward.