Diagnosing P0455 on Your 2020 GMC Sierra
P0455 on your 2020 Sierra means a large EVAP leak. Your 5.3L or 6.2L V8 (or 2.7L turbo, 3.0L diesel) runs fine—this is vapor only. Check for companion code P0449. Gas cap first.
Symptoms
- Check engine light with P0455
- P0449 may also appear
- Fuel smell possible
- Emissions test failure
Causes by Likelihood
- Gas Cap Seal (Very High Likelihood): Degraded. $10–$25.
- Vent Valve Solenoid (Medium Likelihood): GM's known issue. $100–$220 installed.
- Purge Solenoid (Medium Likelihood): Sticking. $110–$240 installed.
- Vapor Line (Low Likelihood): Truck damage. $80–$220.
- Charcoal Canister (Low Likelihood): Saturated. $180–$380 installed.
Warranty
Basic warranty (3yr/36k) has expired. Federal emissions (8yr/80k) covers EVAP through 2028.
Safe to Drive?
Yes. P0455 doesn't affect any engine, 4WD, or towing.