P0446 — EVAP canister vent control: circuit, valve or restriction

P0446 indicates a fault in commanded or monitored EVAP canister vent operation. Depending on the vehicle's monitor, the cause may be a vent-solenoid circuit fault, a valve stuck mechanically or a restricted fresh-air path; it does not by itself prove a leak or condemn the fuel cap. Fuel vapor is flammable: no flame, sparks or improvised pressurization. GM bulletin 23-NA-073 documents dust ingress only for its specified vehicles and markets, not all cars or Romania by default.

Affected system: Powertrain

Symptoms

• Check-engine lamp; vehicle operation may otherwise seem normal.
• On some layouts, the fuel nozzle repeatedly shuts off when tank venting is restricted.
• Fuel odor may accompany an additional vapor leak; P0446 alone does not establish a leak.
• P0442, P0455 or P0449 may coexist and must be interpreted individually rather than treated as synonyms.

Possible causes

• Vent solenoid mechanically stuck open/closed or a blocked canister air inlet/filter.
• Vent-solenoid circuit fault: power/fuse, ground, open or shorted harness, loose terminal or corrosion, depending on control architecture.
• Charcoal canister/hoses contaminated with dust, water or liquid fuel; restricted flow impedes pressure equalization.
• Implausible fuel-tank-pressure (FTP) feedback or purge-command conditions on OEM monitors that infer vent operation from pressure response.
• Only for covered Chevrolet Silverado/GMC Sierra trucks in GM 23-NA-073 (March 2025): severe dust loading of canister/vent solenoid; bulletin regions US, Canada, Middle East and Israel, not automatically Romania.

What to check

• 1. Save all DTCs and freeze-frame before clearing. Separate P0442/P0455 leak monitoring from vent monitoring; with P0449 also evaluate the electrical branch.
• 2. Identify VIN-specific EVAP layout, vent solenoid, FTP sensor, optional filter, capped/capless filler and OEM definition of P0446. Where the monitor is strictly electrical, a pressure test cannot replace circuit diagnosis.
• 3. Engine off and away from ignition sources, inspect connectors, vent-air intake/filter, hoses and canister for blockage, cracks or liquid fuel. A restriction requires finding its origin before replacing a solenoid.
• 4. Examine FTP/tank-pressure data under OEM reference conditions. If the reading remains implausible after the permitted equalization procedure, assess FTP and its hose/electrical path rather than assuming the vent valve failed.
• 5. Command the vent valve open/closed with a suitable bidirectional scan tool. If pressure/flow response is absent, discriminate missing command, stuck valve and blocked line. Audible clicking is not proof of adequate flow.
• 6. During the commanded test check vent power, driver control and grounds using the VIN-specific wiring diagram; missing feed/control identifies the electrical branch, not necessarily a faulty solenoid coil.
• 7. With circuits isolated per OEM, check continuity, shorts to power/ground and coil condition against that exact part's specification. An open/shorted coil identifies the component; sound electrics without airflow point to mechanical restriction.
• 8. If command and electrics pass, inspect filter, canister and vent hoses for restriction and correlate OEM FTP response. For eligible GM vehicles in bulletin 23-NA-073 only, assess the specified auxiliary filter procedure; never generalize it.

Also written as: P0446-00, P044600, PO446 (some scan tools add the fault-type byte, e.g. -00).