P0455 on a 2019 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 2019 Hyundai Sonata

Ranked from 154 NHTSA owner complaints filed for this vehicle.

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1
Faulty EVAP purge valve stuck/leaking
Medium severity
Dealer diagnostics flagged the purge valve after an EVAP code appeared; a purge valve that won't seal is a common large-leak source.
Reported in 1 NHTSA complaint
Parts:purge valve
2
Corroded/rusted fuel filler neck
Medium severity
The dealer initially attributed the leak to filler-neck rust/corrosion in this case, though a second independent shop later found the filler neck intact -- worth ruling out but not confirmed here.
Reported in 1 NHTSA complaint
Parts:fuel filler neck
3
Gas cap left loose, cross-threaded, or missing
Low severity
The large-leak threshold is easily crossed by an unsealed or absent cap; confirm the cap is present, undamaged, and clicks when tightened.
Common cause
Parts:gas cap
4
Disconnected or badly cracked EVAP hose/line
Medium severity
A hose that has popped off a fitting or split open creates a large, easily-detected leak; trace the EVAP lines from canister to intake.
Common cause
Parts:EVAP hose
5
Purge valve stuck open
Medium severity
A purge valve stuck open holds the system at atmospheric pressure, which the large-leak test flags almost immediately.
Common cause
Parts:purge valve
6
Vent valve stuck open or failed
Medium severity
An open vent valve prevents the EVAP system from ever sealing, producing a large-leak result on every monitor run.
Common cause
Parts:vent valve
7
Cracked or split charcoal canister
Medium severity
A significant canister crack behaves like a wide-open leak path; a smoke test pinpoints it quickly.
Common cause
Parts:EVAP canister
8
Corroded fuel filler neck with a hole or perforation
Medium severity
Rust-through on the filler neck is a common large-leak source on older vehicles and can also produce a fuel odor or visible drip.
Common cause
Parts:fuel filler neck
9
Damaged or disconnected fuel tank pressure sensor/wiring
Low severity
A sensor that isn't reporting correctly (or a broken connector) can make the PCM see a leak that isn't really there, or fail to detect the true state of the system.
Common cause
Parts:fuel tank pressure sensor

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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