P0455 on a 2018 Ram 2500

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 2500

Ranked from 2,507 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Restricted/faulty fuel filler neck or vent path allowing large leak
Medium severity
Owner reports the fill neck repeatedly backs up during refueling, indicating a vent-path fault large enough to be flagged as a large leak.
Reported in 1 NHTSA complaint
2
Stuck-open EVAP vent valve
Medium severity
Owner reports the fuel tank fails to hold/release pressure normally and triggers the check engine light - consistent with a vent valve that won't seat, producing a large-leak-sized opening.
Reported in 1 NHTSA complaint
Parts:EVAP vent valve
3
Loose, missing, or faulty gas cap
Low severity
The single most common large-leak trigger; an unseated or damaged cap creates a large, easily-detected leak path.
Common cause
4
Split or disconnected EVAP hose
Medium severity
A hose that pops off or splits open creates a large, easily-detected leak in the EVAP system.
Common cause
5
Purge valve stuck open
Medium severity
A purge valve that fails open allows continuous fresh-air intrusion into the EVAP system, mimicking a large leak.
Common cause
Parts:purge valve
6
Cracked charcoal canister
Medium severity
A larger crack or broken canister seam presents as a large leak during the EVAP monitor test.
Common cause
Parts:charcoal canister

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