P0455 on a 2016 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 2016 Ford Focus Rs

Ranked from 1,143 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Canister purge valve (CPV) failure/stuck open
Medium severity
The same large cluster of purge-valve failures documented for the small-leak code also produces a large-leak pattern: stalling and Ford code P1450 immediately after refueling.
Reported in 8 NHTSA complaints
Parts:purge valve
2
Collapsed or damaged fuel tank restricting venting
Medium severity
A collapsed fuel tank (reported here) disrupts normal EVAP pressure and can trigger a large-leak fault along with stalling.
Reported in 1 NHTSA complaint
Parts:fuel tank
3
Loose, missing, or damaged gas cap
Low severity
A large EVAP leak code is most often a cap left loose or a failed seal — always the first check before chasing hoses.
Common cause
Parts:fuel cap
4
EVAP vent valve stuck open
Medium severity
A vent valve that won't seat lets the system leak to atmosphere continuously, which reads as a large rather than small leak.
Common cause
Parts:vent valve
5
Cracked charcoal canister
Low severity
A significantly cracked canister housing is large enough to fail the large-leak threshold of the EVAP monitor.
Common cause
Parts:charcoal canister
6
Rusted or damaged filler neck
Low severity
A corroded filler neck can open a sizable unsealed path into the EVAP system.
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