P0455 on a 2017 Ford F 150 Supercab

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 2017 Ford F 150 Supercab

Ranked from 1,066 NHTSA owner complaints filed for this vehicle.

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1
Capless "Easy Fuel" filler flap/seal failure
High severity
Multiple owners report fuel vapor smell and gas spraying back out at the capless filler neck; a flap that won't seal fully is a large-enough opening to trip the large-leak EVAP threshold.
Reported in 2 NHTSA complaints
Parts:fuel filler neck seal
2
Purge valve stuck open
Medium severity
One truck stalled repeatedly right after refueling, consistent with the purge valve staying open and pulling raw vapor/air into the intake, which the EVAP monitor can register as a large leak.
Reported in 1 NHTSA complaint
Parts:purge valve
3
EVAP vent valve stuck open
Medium severity
A vent valve stuck fully open provides a wide-open path to atmosphere, the textbook cause of a large EVAP leak code.
Common cause
Parts:vent valve
4
Cracked or disconnected EVAP canister or hose
Medium severity
A split hose or cracked canister housing creates a large enough opening to fail the leak-detection pump/vacuum test outright.
Common cause
Parts:charcoal canister EVAP hose
5
Fuel tank or filler neck corrosion/rust-through
Medium severity
Corrosion can perforate the tank or filler neck, creating a large, constant vapor leak.
Common cause
6
Missing or badly damaged fuel cap seal (non-capless variants)
Low severity
On EVAP systems that retain a cap, a missing, cracked, or wrong cap is the single most common source of a large-leak code.
Common cause
Parts:fuel 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