This code indicates an electrical or functional problem with the evaporative emission control system's vent valve circuit. The vent valve allows fresh air into the EVAP system during purging and seals the system for leak tests; when this circuit fails, the system cannot properly manage fuel vapors.
The valve itself often fails due to dirt, rust, or carbon debris, causing it to stick open or closed electronically.
Corroded, frayed, or disconnected wiring and connectors can disrupt the electrical circuit to the vent valve.
Debris, mud, or spider webs can clog the vent hose or air inlet filter, preventing proper airflow and triggering the circuit code.
A failing canister can release charcoal debris that clogs the vent valve, causing the circuit to read as faulty.
A defective engine computer is extremely rare and almost never the actual cause of this code.
Yes, this code rarely affects engine performance or driveability, but it will cause a failed emissions test.
They are almost certainly wrong. Replacing the PCM is rarely the fix for P0446. The actual cause is almost always a physical failure of the vent valve, corroded wiring, or a clog in the vent hose.
If the vent valve is stuck closed, the EVAP system cannot relieve the pressure built up during refueling, causing the pump nozzle to shut off prematurely.
Yes, spiders, mud, and dust commonly clog the EVAP vent filter and cause the vent valve to stick, triggering this code.