P0446

P0446 is the vent control circuit code — the canister vent solenoid (CVS) isn't responding correctly to the ECU's open/close commands. The vent solenoid is what seals the EVAP system during the leak test; when the ECU wants to pull vacuum on the system, it commands the vent solenoid closed and the purge solenoid open. If the vent solenoid is stuck open, stuck closed, electrically faulted, or clogged with debris, the system can't seal and P0446 trips. The diagnostic ladder: cap first ($5-30 — even though P0446 fingers the vent circuit, a leaking cap can cause the ECU to log the closest related code on some platforms), then multimeter the vent solenoid for proper resistance and supply voltage, then physically remove the vent solenoid and check it for debris. On many vehicles the vent solenoid sits in a position where mud, dust, or insect debris can pack into the vent path and either jam the solenoid or block flow. A smoke test with the vent commanded closed verifies the seal.

By platform: 2007-2014 GM full-size trucks (Silverado, Sierra, Tahoe, Yukon, Suburban) are the textbook P0446 vehicle — the canister vent solenoid mounts near the charcoal canister at the rear of the truck, and the vent line ends near the rear wheel well where it sucks in road dust and mud. The fix is usually a $40-80 vent solenoid plus a clean vent line and sometimes a vent filter retrofit; some shops zip-tie a small filter onto the vent inlet to prevent the next return. 2005-2015 Toyota/Lexus throws P0446 from a worn vent solenoid that's hit end-of-life mechanically, around 100-150k miles; Toyota sells the part for about $80-150. 2003-2010 Ford 4.6L can throw P0446 alongside P0442 when the canister cracks and the vent solenoid gets contaminated by canister dust. 2008-2015 VW/Audi P0446 is usually LDP-related rather than a discrete vent solenoid. 2012+ Hyundai/Kia P0446 is often a CCV (canister close valve) failure — same idea, different acronym. Repair range: $40-150 vent solenoid replacement, $300-500 LDP on VW/Audi.