P0455 on a 2016 Ford Mustang

P0455 means the EVAP system failed a leak check badly enough that the computer sees a large leak or no pressure/vacuum change.

Not your vehicle? See general P0455 info.

Most common causes on the 2016 Ford Mustang

Ranked from 367 NHTSA owner complaints filed for this vehicle.

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1
Cracked EVAP fitting/line at the fuel tank
High severity
Multiple 2016 Mustang owners had a cracked EVAP fitting or fuel-tank seam confirmed by dealer inspection (photos, smoke test), producing a fuel-vapor odor and a leak that sets a small/large EVAP code.
Reported in 5 NHTSA complaints
Parts:fuel tank EVAP hose
2
Faulty EVAP purge valve
High severity
Two owners had a stuck/faulty purge (evaporator) valve - one stuck open causing stalls right after fueling, the other replaced it twice - a recognized recurring-failure part on this platform.
Reported in 2 NHTSA complaints
Parts:purge valve
3
Capless fuel filler neck leaking vapor
High severity
One owner's P0456 was traced to vapor escaping the capless filler neck design used on this generation, requiring the entire filler pipe (no separate gas cap exists) to be replaced.
Reported in 1 NHTSA complaint
Parts:fuel filler neck
4
Failed EVAP vent valve / canister vent solenoid
Medium severity
A vent valve that won't seal prevents the system from holding vacuum/pressure during the EVAP self-test.
Common cause
Parts:vent valve
5
Cracked charcoal canister
Medium severity
A physically damaged canister housing leaks vapor directly and is a standard EVAP leak-code cause.
Common cause
Parts:charcoal canister
6
Loose or damaged fuel filler cap/seal (non-capless trim)
Medium severity
On trims with a conventional cap, a worn or improperly seated seal is the most common trigger for an EVAP leak code.
Common cause
Parts:gas cap

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These causes are aggregated from NHTSA owner complaints and general repair knowledge — this is not a diagnosis. P0455 on your car still needs shop confirmation before any repair.

Common symptoms

Check engine light
Fuel smell
Usually no performance issue
Failed emissions readiness

What to check before replacing parts

Check the gas cap first

Look for: A loose, missing, or cross-threaded cap is by far the most common cause of a large EVAP leak code — if it doesn't click to full tightness or the seal is cracked, that's very likely the whole fault.

Inspect visible EVAP hoses

Look for: A large leak is often obvious: a hose disconnected at a fitting, split open, or chewed through (rodent damage is common) rather than a hairline crack.

Command the purge and vent valves with a scan tool

Look for: A valve that doesn't respond at all when commanded open/closed, or stays open when it should seal, prevents the system from holding pressure/vacuum and reads as a large leak.

Smoke-test the system

Look for: With a large leak, expect an obvious plume of smoke or a clearly audible hiss at the fault location — it should be easy to spot compared to a small-leak diagnosis.

Inspect the canister and filler neck

Look for: A cracked charcoal canister housing or a corroded/rusted-through filler neck (common on older vehicles) can leak enough to prevent the system from ever holding vacuum.

Rather have a pro handle it? Find a vetted local mechanic.

Matching symptoms

Check Engine Light