Tracking P0446 on Your 2020 GMC Sierra
A P0446 code on your 2020 GMC Sierra (T1 platform) indicates an EVAP vent control circuit malfunction. The ECM has detected a fault in the vent valve solenoid circuit. On GM trucks, this solenoid is located near the spare tire area, and P0449 frequently appears as a companion code.
At five to six years old, your Sierra is past GM's 3-year/36,000-mile warranty. The vent valve solenoid is one of the most commonly replaced EVAP components on GM trucks and is a straightforward repair.
Symptoms Found
- Check engine light on with P0446
- Fuel nozzle clicking off during fill-ups
- EVAP readiness monitor incomplete
- P0449 companion code likely present
Most Likely Causes
- Vent Valve Solenoid Failure (High Likelihood): After five-plus years, the vent valve solenoid commonly fails on GM trucks. It's the most frequently replaced EVAP component. Parts $30–$80, labor $75–$165.
- Vent Valve Connector Corrosion (High Likelihood): Five years of rear-underbody exposure corrodes the connector. Cleaning or replacement restores the circuit. Repair costs $45–$125.
- Purge Solenoid Valve Wear (Medium Likelihood): The engine-bay purge solenoid weakens with age. Parts $35–$90, labor $70–$160.
- EVAP Line Deterioration (Medium Likelihood): Frame-mounted lines can be damaged by road debris or towing. Repair costs $55–$200.
- Charcoal Canister Issue (Low Likelihood): Five years with a large fuel tank. Saturation from topping-off habits. Parts $110–$240, labor $90–$195.
DIY Steps
- Scan ECM for all codes — look for P0449 companion
- Locate vent valve solenoid near the spare tire
- Inspect solenoid and connector
- Test solenoid resistance with multimeter
- Apply 12V to test actuation — you should hear a click
- Test purge solenoid in engine bay
- Inspect EVAP lines along the frame
Repair Costs
- Vent valve solenoid: $105–$245
- Connector repair: $45–$125
- Purge solenoid: $105–$250
- EVAP line repair: $55–$200
- Diagnostic fee: $85–$150
Safe to Drive?
Yes. P0446 doesn't affect your Sierra's V8 engine, 10-speed automatic, 4WD, towing, or payload.
Warranty Coverage
GM's basic warranty has expired. The 5yr/60k powertrain warranty may still apply. The federal emissions warranty covers EVAP for 8yr/80k through 2028.