P0455 on a 2020 Ford F 150 Regular Cab

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 2020 Ford F 150 Regular Cab

Ranked from 506 NHTSA owner complaints filed for this vehicle.

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1
Fuel line/hose chafing against the frame near the tank
High severity
One owner found a fuel hose from the top of the tank had dropped and worn a hole against a frame mounting point, causing a large leak.
Reported in 1 NHTSA complaint
Parts:fuel line fuel hose
2
Capless (Easy Fuel) filler neck flapper failing to seal
Medium severity
Ford's capless filler system can let the sealing flapper stick or wear, letting vapor escape; suspect this when a strong gasoline smell appears with an odd fuel-gauge reading and no cap issue.
Reported in 1 NHTSA complaint
Parts:fuel filler neck
3
Fuel tank puncture/impact damage
High severity
A broken driveshaft punctured this truck's fuel tank and dumped gas onto the exhaust; any underbody impact that breaches the tank sets a large EVAP leak code.
Reported in 1 NHTSA complaint
Parts:fuel tank
4
Loose, damaged, or missing fuel filler cap
Low severity
Most common root cause of a large EVAP leak code; check for a cracked/worn cap seal or one left off after fueling.
Common cause
Parts:fuel filler cap
5
Cracked or split EVAP purge valve
Low severity
A purge valve stuck open or leaking lets air/fuel vapor pass at the wrong time and is a very common large-leak trigger.
Common cause
Parts:purge valve
6
Faulty EVAP canister vent valve
Low severity
A vent valve that won't close prevents the system from holding vacuum/pressure during the EVAP leak test.
Common cause
Parts:vent valve
7
Cracked charcoal canister
Medium severity
Road salt and age crack the plastic canister body; look for a canister that won't hold vacuum during smoke testing.
Common cause
Parts:charcoal canister
8
Corroded or rusted fuel filler neck
Medium severity
Rust-through at the filler neck (common on trucks run on salted roads) creates an obvious large leak path.
Common cause
Parts:fuel filler neck

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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