P0455 on a 2018 Ford Fusion

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 2018 Ford Fusion

Ranked from 429 NHTSA owner complaints filed for this vehicle.

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1
Purge valve / purge valve canister failure
Medium severity
Multiple owners had the purge valve (canister purge) replaced -- in one case twice -- and a mechanic specifically diagnosed a failed purge valve/flow valve (with DTC P1450) as the root cause of a stored EVAP fault; a large-leak code often points to the same stuck-open purge path.
Reported in 4 NHTSA complaints
Parts:purge valve
2
EVAP vapor leak in the fuel tank/vent system
Medium severity
One owner explicitly described an 'EVAP system leak' with a vapor leak preventing the vehicle from restarting normally after fueling -- consistent with a large/gross EVAP leak.
Reported in 1 NHTSA complaint
3
Capless fuel filler neck seal/flap failing to seal (freezing in cold weather)
Low severity
One owner reported the capless filler's inner sealing flap freezing shut in sub-zero weather; a filler seal that isn't closing fully is a classic large-leak source.
Reported in 1 NHTSA complaint
Parts:fuel filler neck
4
Loose, worn, or missing gas cap
Low severity
Always the first thing to check for a large EVAP leak code (if equipped with a cap rather than a capless filler).
Common cause
5
Cracked or disconnected EVAP hose/line
Medium severity
A fully disconnected or badly cracked line produces a large, easy-to-detect leak.
Common cause
6
Cracked charcoal (EVAP) canister
Low severity
A significant crack in the canister housing is large enough to trigger the large-leak (P0455) threshold rather than the small-leak (P0442) one.
Common cause
Parts:EVAP canister

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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