P0455 on a 2020 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 2020 Ram 1500

Ranked from 613 NHTSA owner complaints filed for this vehicle.

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1
Fuel tank rollover/vent valve or filler-neck design defect
High severity
The dominant issue in this vehicle's complaint data: a stuck rollover/vent valve in the fuel tank (Ram TSB 14-001-22) disrupts the EVAP vent path and is repeatedly tied by owners/dealers to fill-up and EVAP/canister complaints on this exact truck.
Reported in 15 NHTSA complaints
Parts:fuel tank vent valve fuel filler neck
2
Charcoal canister crack or failure
Medium severity
Two owners had the dealer specifically diagnose or replace the evaporative canister after recurring fueling and check-engine complaints — a large leak points strongly at the canister or its seals.
Reported in 2 NHTSA complaints
Parts:charcoal canister
3
EVAP purge valve stuck open
High severity
One owner had fuel leaking into the canister/purge valve and being dumped into the intake manifold, with the dealer replacing the EVAP canister as a result.
Reported in 1 NHTSA complaint
Parts:purge valve
4
Fuel tank pressure (FTP) sensor fault
Low severity
One complaint noted a 'Service Fuel Sensor' message, consistent with an FTP sensor misreporting to the EVAP monitor.
Reported in 1 NHTSA complaint
Parts:fuel tank pressure sensor
5
Loose or missing gas cap
Low severity
Always the first thing to rule out for a large EVAP leak, even though this vehicle's own data points mainly at the tank/vent-valve defect.
Common cause
Parts:gas cap
6
Disconnected or split EVAP hose
Medium severity
A popped-off or split EVAP line creates an obvious large leak path independent of the tank-valve issue.
Common cause
Parts:evap hose

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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