P0455 on a 2020 Ram 1500 Classic

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 Ram 1500 Classic

Ranked from 613 NHTSA owner complaints filed for this vehicle.

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1
Faulty fuel filler neck / rollover check valve (5th-gen Ram TSB)
Medium severity
Multiple complaints describe fuel splashing back and repeated pump shutoffs while refueling due to a stuck rollover valve/pressure buildup in the filler neck — a documented issue on 5th-generation Ram trucks with an active TSB.
Reported in 4 NHTSA complaints
Parts:fuel filler neck
2
Fuel-saturated or failed EVAP charcoal canister
Medium severity
Several of the same complaints report the canister/purge system being soaked with liquid fuel backing up from the filler neck, and dealers replacing the canister as the fix.
Reported in 3 NHTSA complaints
Parts:EVAP charcoal canister
3
Purge valve leaking or stuck open
Low severity
One complaint describes fuel leaking into the purge valve and dumping into the intake manifold during refueling, consistent with a compromised purge valve seal.
Reported in 1 NHTSA complaint
Parts:purge valve
4
Loose, cross-threaded, or worn gas cap
Low severity
The single most common EVAP leak source generally; a cap that doesn't seal or click fully lets the system fail its leak test. Try a new cap first.
Common cause
Parts:gas cap
5
Cracked or brittle EVAP vapor line/hose
Low severity
Age-hardened rubber lines under the vehicle crack and leak vapor; smoke-test the EVAP system to pinpoint the leak location.
Common cause
Parts:EVAP hose
6
Vent valve (canister vent solenoid) stuck open or leaking
Low severity
The vent valve must seal the system for the leak test to pass; a stuck-open valve produces a constant small/large leak code depending on how it fails.
Common cause
Parts:vent valve
7
Rusted or corroded fuel filler neck (general aging, distinct from the rollover-valve TSB)
Medium severity
Corrosion or physical damage to the filler neck, common in road-salt regions, can create a large EVAP leak path on its own; inspect the neck and hose clamps.
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