P0446: EVAP System Vent Control Circuit

The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. The vent valve is normally open and closes for the leak test. By its wording P0446 is its control circuit, and Ford uses it that way for open and shorted circuits. GM, however, uses P0446 for vent system performance – a blocked vent path: while purging with the vent valve open, the tank must not build up vacuum; more than 2989 Pa for 5 s before 4 litres have been purged sets the code, MIL after two trips. GM reports vent circuit faults as P0449, P0498 and P0499. A blocked vent makes refuelling difficult.

Low severity. Can I keep driving?Yes, you can keep using the car. With a blocked vent, the pump nozzle may keep clicking off when you refuel and the tank may be left under vacuum, so do not put it off too long.

Symptoms

Check engine light on
Refuelling problems, nozzle clicks off early (blocked vent)
Hissing when opening the fuel cap (vacuum)
EVAP leak test does not run

Most likely causes

Vent valve or filter blocked by dirt, dust or water (GM reading)
Vent valve electrically faulty, coil open or shorted (Ford reading)
Connector or wire to the vent valve corroded or open
Canister clogged with charcoal or liquid (overfilling)
Vent hose kinked or blocked by an insect nest

What to check, in order

Start with the simplest. You can tick off each step.

Start with the fuel cap: tighten it fully and check its seal
Inspect the hoses and connections around the tank and the charcoal canister
Use the scanner to test the purge and vent solenoid valves
Run a smoke test to find small leaks

Good to know

Repair difficulty: medium
It affects emissions.

What each character of P0446 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
4: Emissions
46: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0446?

Yes, you can keep using the car. With a blocked vent, the pump nozzle may keep clicking off when you refuel and the tank may be left under vacuum, so do not put it off too long.

What causes code P0446?

The most common causes are: vent valve or filter blocked by dirt, dust or water (GM reading); vent valve electrically faulty, coil open or shorted (Ford reading); connector or wire to the vent valve corroded or open.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.