Common Checks
- Check the fuel cap or capless filler seal first.
- Inspect small EVAP hoses and the canister vent path.
- Smoke-test the system because very small leaks are hard to find visually.
Diagnostic trouble code
P0456 EVAP System Very Small Leak Detected
The EVAP monitor detects a very small vapor leak.
EVAP Leak & Purge CodesCommon Repairs
- Clean or replace the cap/filler seal if it does not hold pressure.
- Replace cracked small-diameter EVAP hoses.
- Repair leaking purge, vent, or canister components found by smoke test.
Mustang Notes
- A very small leak can take multiple drive cycles to confirm after repair.
Model-Year Applicability
Listed for 1996 and newer traditional gasoline Mustang pages in this first-pass catalog. Engine, calibration, and Ford-specific codes may narrow that range as more service data is added.