P0455 on a 2010 Chevrolet Impala
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 2010 Chevrolet Impala
Ranked from 441 NHTSA owner complaints filed for this vehicle.
- 1
Faulty fuel filler neck flap/seal (fails to reseal, allowing continuous air ingress)
Medium severityAn owner documented the filler-neck flap that should remain closed staying open, a leak path large enough to consistently fail the EVAP monitor's large-leak test.
Reported in 1 NHTSA complaintParts:fuel filler neck - 2
Damaged or leaking fuel line
High severityFuel lines found wet and dragging on the ground with the fuel gauge steadily dropping describe a substantial, continuous leak consistent with a large-leak EVAP code and a fire risk.
Reported in 1 NHTSA complaintParts:fuel line - 3
Missing, loose, or badly damaged gas cap
Low severityThe most common large-leak cause on any vehicle; a cap not sealing at all fails the large-leak test outright.
Common causeParts:fuel cap - 4
Cracked or split charcoal canister
Medium severityA larger canister failure produces a large- rather than small-leak code.
Common causeParts:charcoal canister - 5
Purge or vent valve stuck open
Medium severityA valve unable to close at all prevents the EVAP system from holding pressure/vacuum during the monitor's test.
Common cause - 6
Corroded or rusted fuel tank/filler neck
Medium severityRust perforation on an older vehicle creates a large opening in the vapor system.
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.