P0455 on a 2021 Ram 1500

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 2021 Ram 1500

Ranked from 659 NHTSA owner complaints filed for this vehicle.

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1
Restricted or malfunctioning filler neck / EVAP vent path
Medium severity
Three complaints describe fuel-nozzle click-off, filler-neck blowback, and tank overflow on this truck -- symptoms of a vent/pressure path that isn't behaving normally and can present alongside a large-leak EVAP code.
Reported in 3 NHTSA complaints
Parts:filler neck EVAP vent hose
2
Fuel tank internal vent/rollover valve failure
Medium severity
Two complaints trace fueling problems directly to a failed valve inside the fuel tank -- one truck had the tank replaced for a 'bad valve inside it' -- a large stuck-open vent path is consistent with a gross EVAP leak.
Reported in 2 NHTSA complaints
Parts:fuel tank vent valve
3
Loose, cracked, or missing gas cap
Low severity
By far the most common cause of a large/gross EVAP leak; a cap that isn't sealing produces exactly the size of leak this code flags.
Common cause
Parts:gas cap
4
Disconnected or split EVAP hose
Medium severity
A fully detached or split hose presents a large, easy-to-find leak; smoke-test the EVAP system to locate it.
Common cause
Parts:EVAP hose
5
Purge valve stuck open
Medium severity
A purge valve stuck fully open lets the system leak down immediately during the monitor, producing a large-leak result.
Common cause
Parts:purge valve
6
Vent valve (canister close valve) failure
Medium severity
A vent valve that won't close prevents the EVAP system from sealing at all during the self-test, which reads as a large leak.
Common cause
Parts:EVAP vent valve

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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