2022 Buick Envision P0456 Code: Very Small EVAP Leak Diagnosis Guide

P0456 on Your 2022 Buick Envision

A P0456 code on your 2022 Buick Envision means the ECM has detected a very small leak—approximately 0.020 inches—in the EVAP system. The second-generation Envision (2021+) uses GM's EVAP architecture with electronic vent and purge valve controls, powered by a 2.0L turbocharged four-cylinder engine producing 228 hp.

At three-plus years old, your Envision is at the beginning of the window where EVAP component wear can start to appear, though simpler causes remain most likely.

Common Causes

1. Gas cap seal wear (33%) — Three years of regular fueling degrades the rubber seal. The top suspect to investigate.
2. Vent valve solenoid failure (24%) — GM's most commonly failed EVAP component. It controls airflow through the charcoal canister and can stick or develop internal leaks.
3. EVAP hose or connection looseness (16%) — Quick-connect fittings and rubber lines can work loose from thermal cycling and vibration.
4. Purge valve seepage (13%) — The engine-bay purge solenoid may develop a slight internal leak when commanded closed.
5. Charcoal canister issue (9%) — Road debris or moisture intrusion can compromise the canister.
6. Fuel tank seal (5%) — Slow gasket degradation over time.

Diagnostic Steps

1. Gas cap test — New OEM cap ($12–$25), clear code, drive for a week.
2. Visual inspection — Check accessible EVAP hoses and connections for damage or looseness.
3. Smoke test — Professional smoke testing ($50–$100) reveals the exact leak.
4. GDS2 diagnostics — GM dealer tool monitors EVAP system parameters in real time.
5. Component testing — Individual vent valve solenoid and purge valve testing.

Repair Costs

• Gas cap: $12–$25 (DIY)
• Vent valve solenoid: $130–$260
• EVAP hose repair: $80–$200
• Purge valve: $120–$250
• Charcoal canister: $230–$450

Warranty Coverage

Your 2022 Buick Envision's 3-year/36,000-mile basic warranty extends through 2025—check your mileage. The federal emissions warranty covers EVAP components for 8 years/80,000 miles through 2030. Contact your Buick dealer to verify coverage before paying out of pocket.