P0455 on a 2019 Subaru Ascent
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 Subaru Ascent
Ranked from 433 NHTSA owner complaints filed for this vehicle.
- 1
Persistent EVAP/fuel-system leak producing strong gasoline vapor in cabin/garage
Medium severityMultiple owners independently report strong raw-fuel odor entering the cabin at idle or after parking, consistent with an EVAP leak large enough to register as a gross leak.
Reported in 6 NHTSA complaints - 2
Cracked/leaking EVAP fuel vapor canister
Medium severityA dealer directly diagnosed a leak in the fuel vapor canister on one of these vehicles, which recurred even after repair — large enough to be readily detected.
Reported in 1 NHTSA complaintParts:EVAP canister - 3
Loose, missing, or improperly seated gas cap
Low severityThe single most common cause of a large/gross EVAP leak code; check first.
Common causeParts:gas cap - 4
Cracked, disconnected, or chafed-through EVAP hose/line
Medium severityA fully disconnected or badly cracked line produces enough open area to fail the gross-leak monitor.
Common causeParts:EVAP hose - 5
Purge or vent valve stuck open
Medium severityA valve stuck fully open prevents the system from ever sealing, reading as a large leak.
Common cause - 6
Rusted or corroded fuel filler neck
Low severityAdvanced filler-neck corrosion can perforate enough to fail the gross-leak test outright.
Common causeParts: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.