P0446
Evaporative Emission System Vent Control Circuit
- Severity
- Low
- Driving
- Drivable — book it in
A fault in the evaporative emissions vent control circuit. The vent valve lets fresh air into the charcoal canister so the trapped vapour can be drawn out, and closes so the system can be pressure-tested for leaks. Stuck closed, the tank cannot breathe; stuck open, the leak test always fails.
Possible causes
- CommonFailed vent valve or solenoid
- CommonCorroded connector - the vent valve is usually mounted under the vehicle
- CommonVent filter blocked with dirt, or an insect nest in it
- CommonDamaged wiring under the vehicle
- PossibleDebris from a degraded charcoal canister jamming the valve
- RareFailed control module driver
What you might notice
- Check engine light on
- Failed emissions test
- Hissing when the fuel cap is opened
- Fuel tank sounding pressurised
- Difficulty filling the tank - the pump cutting off repeatedly
- Usually no drivability symptom
What to check, in order
- Inspect the vent valve and its filter underneath the vehicle. Corrosion and blockage are the two common causes, and insect nests in the vent filter are a genuine and frequent one.
- Check the connector for corrosion and water - this valve takes constant road spray.
- Measure the valve winding resistance against specification.
- Check whether the valve opens and closes when commanded.
- Note that EVAP monitors only run in particular conditions of fuel level and temperature, so confirming a repair can take several journeys.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Auxiliary emission controls
P0400P0401P0402P0403P0404P0405P0406P0407P0408P0409P0410P0411P0412P0413P0414P0415P0416P0417P0418P0419P0420P0421P0422P0423P0424P0425P0426P0427P0428P0429P0430P0431P0432P0433P0434P0435P0436P0437P0438P0439P0440P0441P0442P0443P0444P0445P0446P0447P0448P0449P0450P0451P0452P0453P0454P0455P0456P0457P0458P0459P0460P0461P0462P0463P0464P0465P0466P0467P0468P0469P0470P0471P0472P0473P0474P0475P0476P0477P0478P0479P0480P0481P0482P0483P0484P0485P0486P0487P0488P0489P0490P0491P0492P0493P0494P0495P0496P0497P0498P0499