P0455 on a 2016 Kia Optima

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 Kia Optima

Ranked from 748 NHTSA owner complaints filed for this vehicle.

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1
Disconnected, cracked, or split EVAP/fuel vapor hose
Medium severity
Owners describe fuel-hose leaks and persistent fuel odor, consistent with a large opening in the vapor line rather than a pinhole leak.
Reported in 2 NHTSA complaints
Parts:EVAP hose
2
Fuel tank vent (ORVR) valve or filler-neck check valve stuck open
Medium severity
The same complaint of fuel gurgling back out at the pump nozzle points to a filler/vent valve malfunction large enough to also register as a gross EVAP leak.
Reported in 1 NHTSA complaint
Parts:fuel tank vent valve filler neck check valve
3
Missing, loose, or badly damaged gas cap
Low severity
A cap that isn't tightened, is cracked, or is simply missing produces a large, easily-detected EVAP leak; check/replace first.
Common cause
Parts:fuel filler cap
4
Purge valve stuck open
Medium severity
A purge solenoid stuck fully open holds the EVAP system at atmospheric pressure and cannot pass the large-leak test.
Common cause
Parts:purge valve
5
Cracked or split charcoal canister
Medium severity
A significant crack (versus a hairline one) in the canister housing produces a leak large enough to fail the gross-leak monitor.
Common cause
Parts:charcoal canister
6
Rusted-through fuel filler neck
Low severity
Advanced corrosion can perforate the filler neck enough to create a large, continuous vapor 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