P0455 on a 2016 Chevrolet Impala Eco Eassist

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 Chevrolet Impala Eco Eassist

Ranked from 786 NHTSA owner complaints filed for this vehicle.

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1
EVAP vent valve stuck closed / restricted tank venting
Medium severity
A complaint describes the tank refusing to fill past about three-quarters capacity, a symptom of a stuck-closed EVAP vent valve or restricted vent line; a valve failing this way can also fail to seal for the large-leak test.
Reported in 1 NHTSA complaint
Parts:EVAP vent valve
2
Emissions system fault flagged after an auto-stop stall
Low severity
One owner's dash displayed an emissions-control message tied to a stall coming out of auto-stop, pointing at the emissions monitoring system as worth checking alongside the code.
Reported in 1 NHTSA complaint
3
Loose, damaged, or missing gas cap
Low severity
A non-sealing cap is the single most common large-EVAP-leak trigger and the first thing to rule out.
Common cause
Parts:gas cap
4
Cracked or disconnected EVAP hose/line
Medium severity
A split or popped-off vapor line creates an obvious large leak that fails the EVAP monitor immediately.
Common cause
Parts:EVAP hose
5
Charcoal canister crack
Medium severity
A significantly cracked canister can't hold vapor pressure at all, presenting as a large leak.
Common cause
Parts:charcoal canister
6
Purge valve stuck open
Medium severity
A purge valve that fails fully open connects the EVAP system straight to intake vacuum, which the system reads as a large leak.
Common cause
Parts:purge valve
7
Corroded or rusted filler neck
Low severity
Advanced corrosion can open a gap at the filler neck large enough to fail the large-leak portion of the test.
Common cause
Parts: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