P0446: EVAP Vent Control Circuit
P0446 means the car's evaporative emission (EVAP) system has a problem with its vent valve: either the valve's electrical circuit is faulty or the vent path is blocked, depending on the manufacturer. It is usually not urgent for the engine, but it turns on the check engine light and can cause an emissions test failure.
You can keep driving
The engine is not put into limp mode by this code, so the car can normally be driven. A blocked vent can make refueling difficult, and the fault should be fixed to clear the light and pass an emissions test.
What it means
The EVAP system catches fuel vapor from the tank in a charcoal canister so it does not escape into the air. A purge valve lets the engine draw that vapor off, and a vent valve opens the canister to fresh air. The vent valve is normally open and closes during the system's leak test. The code's wording points to the vent valve's control circuit, and Ford uses it that way for open or shorted circuits. GM uses P0446 for vent system performance, meaning a blocked vent path: if the tank builds up more than 2989 Pa of vacuum for 5 seconds before 4 liters of vapor have been purged, the code is set. The check engine light (MIL) comes on after two trips where the fault is detected. GM reports vent circuit faults under P0449, P0498 and P0499 instead.
Likely causes
- Vent valve or filter blocked by dirt, dust or water (GM reading)Very likely
A blocked vent path lets vacuum build in the tank while the engine draws vapor off, which is exactly what sets the code on GM vehicles.
- Vent valve electrically faulty, coil open or shorted (Ford reading)Possible
If the valve's internal coil is open or shorted, the control module sees a circuit fault and sets the code.
- Connector or wire to the vent valve corroded or openPossible
Corrosion or a broken wire interrupts the control signal even if the valve itself is fine.
- Canister clogged with charcoal or liquid (overfilling)Possible
Charcoal or liquid fuel in the canister can restrict airflow through the vent path.
- Vent hose kinked or blocked by an insect nestLess likely
A pinched or plugged hose stops fresh air from reaching the canister.
What you may notice
- Check engine light on
- Refueling problems, with the nozzle clicking off early (blocked vent)
- Hissing when opening the fuel cap (vacuum in the tank)
- EVAP leak test does not run
What to check, cheapest first
- 1Read the code and any related codes (P0447, P0448, P0449, P0498, P0499, P0455) with a scan tool to see which reading applies to your vehicle. · you can do it
- 2Look at the vent hose and the area around the canister for kinks, damage, dirt, water or insect nests. · you can do it
- 3Inspect the vent valve connector and wiring for corrosion, loose pins or broken wires. · you can do it
- 4Test the vent valve electrically, checking whether its coil is open or shorted, and whether it opens and closes on command. · mechanic
- 5Check airflow through the vent path and the canister for blockage by dirt, charcoal or liquid fuel. · mechanic
- 6After the repair, clear the code and complete a drive cycle so the EVAP test runs and confirms the fix. · mechanic
Related codes
Frequently asked questions
Can I keep driving with P0446?+
Usually yes. The code does not cause limp mode, but the check engine light stays on and a blocked vent can make refueling difficult.
Can a gas cap cause P0446?+
The data lists the vent valve, wiring, canister and vent hose as causes, not the cap. A cap problem more commonly sets other EVAP leak codes such as P0455.
Will P0446 pass an emissions test?+
Probably not. The code is emissions-relevant and keeps the check engine light on, and the EVAP leak test may not run until it is fixed.
Can I fix it myself?+
Often yes. The repair is rated medium difficulty and takes roughly 0.5 to 2 hours, for example cleaning a blocked vent or replacing the vent valve.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10