P0455 on a 2020 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 2020 Ford F 150 Supercab
Ranked from 506 NHTSA owner complaints filed for this vehicle.
- 1
Disconnected or cracked large EVAP/fuel vapor hose
High severityA visible gasoline leak from a hose at the top of the fuel tank on this truck is large enough to also register as a large EVAP leak.
Reported in 1 NHTSA complaint - 2
Loose, missing, or improperly seated gas cap
Low severityThe single most common large-leak trigger; a fuel-vapor smell noted after fueling on this truck is consistent with an inadequately sealed cap.
Reported in 1 NHTSA complaintParts:fuel filler cap - 3
Purge valve stuck open
Medium severityA purge valve stuck open prevents the system from holding vacuum/pressure during the monitor, reading as a large leak.
Common causeParts:EVAP purge valve - 4
Vent valve or canister failure
Medium severityA vent valve or canister that won't seal produces a large, easily detected leak.
Common cause - 5
Fuel tank pressure sensor fault
Low severityA faulty sensor can falsely report a large leak even when the system is sealed.
Common cause - 6
Damaged or corroded fuel filler neck
Low severityPhysical damage or rust-through at the filler neck opens a large vapor path.
Common causeParts: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.