Investigating P0455 on Your 2021 Ford Mustang
A P0455 on your 2021 Ford Mustang means the PCM detected a large EVAP system leak. Your S550 Mustang is out of Ford's basic warranty but covered by the federal emissions warranty. Whether you have the 5.0L Coyote V8, 2.3L EcoBoost, or Mach 1's 5.0L, the EVAP system is the same. Gas cap first.
Signs Present
- Check engine light with P0455
- Faint fuel odor near the rear
- Gas cap seal wearing after 4–5 years
- Emissions test failure
Causes Ranked
- Gas Cap Seal (Very High Likelihood): Worn or loose seal. $10–$25 OEM replacement.
- Canister Vent Solenoid (Medium Likelihood): Ford vent valve sticking. $130–$240.
- EVAP Hose (Medium Likelihood): Heat exposure from the performance exhaust accelerates deterioration. $80–$220.
- VMV (Low Likelihood): Ford purge valve. $100–$200.
- Fuel Tank Gasket (Low Likelihood): Seal at the sender. $100–$250.
Diagnostic Steps
Replace the gas cap ($10–$25). Clear the code with FORScan and drive 2–3 cycles. If P0455 returns, a smoke test will pinpoint the leak.
Warranty Coverage
Ford's basic warranty has expired. The federal emissions warranty (8yr/80k) covers EVAP through 2029. Contact your dealer for free repair eligibility.
Safe to Drive?
Yes. P0455 doesn't affect the Mustang's engine performance, transmission, or handling dynamics.