P0455 on a 2016 Ford Focus

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

Ranked from 1,187 NHTSA owner complaints filed for this vehicle.

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1
Canister purge valve (CPV) stuck open/failed
Medium severity
The dominant documented issue on this exact vehicle: a stuck-open CPV (Ford recalls 18S32/19S22, campaign 24N07) leaves the EVAP system unable to seal at all, producing a large-leak code along with rough idle, hard restarts after fueling, and stalling across many owner reports.
Reported in 14 NHTSA complaints
Parts:canister purge valve
2
Deformed/collapsed fuel tank from failed purge valve
Medium severity
A stuck-open purge valve that fails to bleed vacuum from the tank can physically deform/collapse it, as documented on this vehicle after recall repairs — a collapsed tank cannot hold the pressure needed to pass the large-leak test.
Reported in 2 NHTSA complaints
Parts:fuel tank canister purge valve
3
Missing or badly damaged gas cap / capless flap
Low severity
A cap left off, or a capless filler flap that won't close, is an unmistakable large-leak trigger and the first thing to rule out.
Common cause
Parts:fuel cap
4
Disconnected or split large EVAP hose
Medium severity
A popped-off or split hose creates a wide-open path to atmosphere that the monitor reads immediately as a large leak.
Common cause
Parts:EVAP hose
5
Vent valve stuck open
Medium severity
A canister vent solenoid failed open prevents the EVAP system from sealing under any condition, guaranteeing a large-leak result.
Common cause
Parts:vent valve
6
Corroded/rusted filler neck or tank seam
Medium severity
Perforation at the filler neck or a tank seam creates a large, constant leak path, more common on older or salt-belt vehicles.
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