Tracking P0456 on Your 2020 Silverado
Your 2020 Silverado (T1XX platform, second model year of the redesign) has flagged P0456—a very small EVAP leak at 0.020 inches. The full-size truck's EVAP system is shared across the 2.7L turbo, 5.3L V8, 6.2L V8, and 3.0L Duramax diesel. At 5–6 years old, the gas cap and vent valve solenoid are the prime suspects.
Symptoms
- Check engine light on (steady)
- P0456 stored
- No power or towing issues
- No fuel economy change
- Gas cap may feel worn
Suspects
- Gas Cap Seal (High Likelihood): Five years of tightening and loosening wears the rubber seal. Replace for $10–$15.
- Vent Valve Solenoid (High Likelihood): Near the spare tire. GM's most common EVAP component failure. Multiple TSBs exist. $80–$220.
- Purge Solenoid (Medium Likelihood): Engine bay location, heat-related degradation over time. $80–$200.
- EVAP Line Micro-Crack (Medium Likelihood): Rubber lines harden after 5+ years. Towing vibration accelerates this. $100–$250.
- Charcoal Canister (Low Likelihood): Fuel overfilling damage or age degradation. $200–$400.
Diagnosis
- Replace the gas cap ($10–$15)—the cheapest fix to try first
- Clear the code and complete a drive cycle
- If code returns, inspect the vent valve solenoid near the spare tire
- Smoke test for the micro-leak location
- Check for companion codes (P0449 often accompanies EVAP issues on GM trucks)
Cost Breakdown
- Gas cap: $10–$15
- Vent valve solenoid: $80–$220
- Purge solenoid: $80–$200
- EVAP hose: $100–$250
- Charcoal canister: $200–$400
Can I Tow?
Yes. P0456 has absolutely no effect on towing, hauling, engine power, or any truck capability.
DIY Guide
GM's 3yr/36k expired around 2023. Federal emissions (8yr/80k) covers EVAP through 2028—check your mileage. For DIY, the gas cap is obvious. The vent valve solenoid near the spare tire is accessible from underneath with basic hand tools—a common DIY repair for Silverado owners with plenty of YouTube guides available.