P0455 on a 2018 Ford Focus Rs

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 Ford Focus Rs

Ranked from 743 NHTSA owner complaints filed for this vehicle.

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1
Stuck-open Canister Purge Valve (CPV)
Medium severity
A very large cluster of owners describe the purge valve sticking open (the pattern behind NHTSA recall 18V-735), producing EVAP fault codes, stalling after refueling, and hard restarts.
Reported in 13 NHTSA complaints
Parts:canister purge valve
2
Failed EVAP canister/valve assembly requiring repeat recall replacement
Medium severity
One owner had the EVAP canister valve assembly replaced three separate times under Ford's recall for the same stalling/EVAP-fault symptoms, indicating the canister/valve assembly is prone to repeat, larger-scale failure.
Reported in 2 NHTSA complaints
Parts:EVAP canister
3
EVAP purge vapor line obstruction or disconnection
Medium severity
Scan data specifically flagged the EVAP purge vapor line as obstructed and called for replacing the canister purge control valve.
Reported in 1 NHTSA complaint
Parts:EVAP purge line
4
Loose, damaged, or missing fuel filler cap
Low severity
A cap that fails to seal is the most common cause of a large EVAP leak and is the first thing to check.
Common cause
Parts:fuel cap
5
Cracked or disconnected EVAP hose/line
Medium severity
A fully disconnected or split EVAP line creates a large, unmistakable vapor leak that will set P0455 quickly.
Common cause
Parts:EVAP hose
6
Rusted or damaged fuel filler neck
Low severity
A corroded filler neck can develop a hole or a poor seal against the cap flange, producing a large, continuous leak.
Common cause

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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