You filled up your 2022 Ascent and within a few miles, the check engine light appeared. The P0456 code indicates a small EVAP system leak. The timing after refueling suggests a simple cause—and potentially a simple fix.
What P0456 Means
The P0456 code indicates "Evaporative Emission Control System Small Leak Detected." The EVAP system captures fuel vapors, and P0456 triggers when a leak roughly the size of a 0.020-inch hole is detected.
Why After Filling Up?
Several refueling-related causes:
- Gas cap not clicked - Most common cause
- Cross-threaded cap - Installed at an angle
- Debris on cap seal - Dirt preventing seal
- Overfilling tank - Fuel in EVAP system
- Cap seal worn - Gasket deteriorated
The Easy Fix
- Stop somewhere safe
- Remove gas cap completely
- Inspect rubber seal for damage or debris
- Reinstall until you hear 3+ clicks
- Drive normally for 50+ miles
- Light often turns off automatically
If Light Remains
After properly securing the cap, if the light persists:
- Try a new OEM gas cap
- Have an EVAP smoke test performed
- Check for cracked EVAP hoses
- Inspect vent and purge valves
Small Leak Sources
- Gas cap - Most common
- EVAP hose cracks - Age-related
- Canister vent valve - Doesn't seal completely
- Filler neck seal - O-ring worn
Repair Costs
- Gas cap: $20-$50
- EVAP smoke test: $100-$150
- EVAP hose repair: $100-$250
- Vent valve: $150-$350