P0446

The P0446 code indicates a malfunction in the EVAP vent control circuit. The vent valve controls the flow of fresh air into the EVAP system's charcoal canister. During normal driving, the vent valve is open to allow fuel vapors to be stored in the canister. During EVAP self-tests, the ECM closes the vent valve to seal the system and check for leaks. When the ECM detects the vent circuit isn't responding properly, it sets this code.

This code is extremely common on GM vehicles (Chevrolet, GMC, etc.) and is one of the most frequently reported EVAP system faults. A telltale symptom beyond the Check Engine Light is difficulty filling the gas tank—the pump nozzle may click off repeatedly because the tank can't vent properly. You might also hear a hissing sound when removing the gas cap, indicating abnormal pressure in the tank.

The vent valve is typically located near the charcoal canister under the vehicle or near the rear wheel well. A common non-electrical cause is spider webs or insect nests blocking the vent filter—a surprisingly frequent occurrence. Check and clean the vent filter first, then test the vent solenoid electrically. Replacement is usually straightforward and inexpensive, with the solenoid costing $20–$80. Professional repair runs $150 to $400.

Severity

Symptoms

• •Check Engine Light is on
• •Difficulty at the gas pump—fuel nozzle clicks off repeatedly
• •Slight fuel odor near the rear of the vehicle
• •Minor decrease in fuel economy
• •Failed emissions inspection
• •Occasional hissing sound when opening the gas cap

Likely Causes

Estimated Cost

Common Fixes

1. Replace the EVAP vent valve/solenoid
2. Clean or replace clogged vent lines and filters
3. Repair damaged wiring or connectors at the vent valve
4. Clean debris from the charcoal canister vent port
5. Replace the charcoal canister if internally restricted

Shop Parts

Related Codes