P0455 on a 2011 Hyundai Sonata
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 2011 Hyundai Sonata
Ranked from 3,371 NHTSA owner complaints filed for this vehicle.
- 1
EVAP purge or vent control valve stuck open
Medium severityThe same vent/purge valve fault reported on this vehicle (explicit P0449 code plus a hard-to-fill/venting symptom) can hold the vapor path open wide enough to register as a large rather than small leak.
Reported in 2 NHTSA complaints - 2
Fuel tank pressure (FTP) sensor fault
Medium severityA faulty FTP sensor (one complaint reports an explicit P0451 code) is part of the same EVAP monitoring circuit and can cause the system to falsely register a large leak.
Reported in 1 NHTSA complaint - 3
Loose or improperly seated gas cap
Low severityThe most common large-leak trigger; a cap not tightened to the click or with a cracked seal fails the EVAP monitor outright.
Common causeParts:gas cap - 4
Cracked, disconnected, or split EVAP hose/line
Medium severityA fully split or popped-off line creates a large, easily detected leak; trace vapor lines from tank to canister to purge valve.
Common cause - 5
Charcoal canister crack
Medium severityA significantly cracked canister can leak enough vapor to trigger the large-leak threshold.
Common causeParts:charcoal canister - 6
Rusted or damaged filler neck
Medium severitySignificant corrosion or a punctured filler neck creates an obvious, large vapor leak near the fuel door.
Common causeParts: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.