Summary
P0446 means the PCM detected a fault in the EVAP vent valve circuit — the valve that allows fresh air into the charcoal canister during purge cycles and seals the system during leak tests. The most common cause is a faulty vent valve solenoid (50%), followed by a blocked vent hose or filter (25%) and wiring issues (15%). The vent valve is usually near the charcoal canister at the rear of the vehicle. Replacement costs $20–$80 for the part.
Severity: Low — emissions only
Safe to drive: Yes — no drivability impact
Repair cost: $20–$200 depending on cause
DIY difficulty: Moderate
What does P0446 mean?
The EVAP vent valve (also called the canister vent solenoid or CVS) controls airflow into and out of the charcoal canister. During normal operation, the vent is open so fresh air can enter the canister as fuel vapors are purged into the engine. During the EVAP leak test, the vent closes to seal the system.
P0446 sets when the PCM detects an electrical or functional fault with this vent valve circuit. This could mean the valve is stuck open (system can't seal for the leak test), stuck closed (canister can't breathe), or has a circuit problem (open/short in wiring).
The distinction from P0455/P0442: those codes say "the system leaked." P0446 says "the vent valve circuit has a fault." The vent valve fault may cause secondary leak codes if the system can't seal during testing.