P0455 on a 2018 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 2018 Ram 1500

Ranked from 644 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Stuck-open fuel tank rollover-vent valve
Medium severity
The same widely reported Ram tank-venting defect can fail fully open rather than just restricting flow, giving the EVAP monitor a large, continuous leak path; dealers have replaced entire tanks for this.
Reported in 13 NHTSA complaints
Parts:fuel tank vent valve fuel tank
2
Charcoal canister crack or saturation
Medium severity
An owner linked repeated fill failures to the vapor canister/fuel-system design; a cracked housing or fuel-soaked canister creates a large unmetered vapor path.
Reported in 1 NHTSA complaint
Parts:charcoal canister
3
Loose, missing, or damaged gas cap
Low severity
The classic P0455 large-leak trigger — if the cap was left off or its seal is torn, the very next EVAP monitor fails.
Common cause
Parts:fuel cap
4
Cracked or split EVAP hoses/lines
Medium severity
A fully split vapor line (rather than a pinhole) produces the larger leak rate that trips P0455 specifically.
Common cause
5
Rusted/corroded filler neck
Medium severity
A rusted-through filler neck section is large enough to register as a large leak rather than a small one.
Common cause
Parts:fuel filler neck
6
Purge valve stuck open
Medium severity
A purge valve permanently stuck open lets full manifold vacuum bleed through the EVAP system, mimicking a large leak.
Common cause
Parts:purge valve

Part links go to Amazon search results for this vehicle. As an Amazon Associate, WrenchConnect earns from qualifying purchases — always confirm fitment for your exact trim and engine before ordering.

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