P0455 on a 2015 GMC Canyon

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 2015 GMC Canyon

Ranked from 318 NHTSA owner complaints filed for this vehicle.

Sort by:

1
Fuel tank / line connection leak at the pump module
High severity
One owner found fuel actively leaking from the feed/return line connections at the in-tank pump module — a gross leak large enough to set a large-leak EVAP code.
Reported in 1 NHTSA complaint
2
EVAP monitor/gas cap seal fault (false 'tighten cap' warning)
Medium severity
One owner replaced the fuel cap three times without resolving a persistent warning, pointing to a filler-neck seal or EVAP sensor fault rather than the cap.
Reported in 1 NHTSA complaint
Parts:fuel cap
3
Loose, damaged, or missing gas cap
Low severity
The most frequent cause of a large EVAP leak code; verify the cap seats and clicks fully.
Common cause
Parts:fuel cap
4
Cracked or disconnected EVAP line
Medium severity
A fully disconnected or split line produces the large-leak threshold quickly during the monitor's test.
Common cause
5
Vent valve stuck open
Medium severity
A vent valve that fails open prevents the system from sealing at all, a classic large-leak trigger.
Common cause
Parts:vent valve
6
Purge valve failure
Medium severity
A purge valve that leaks continuously prevents the EVAP system from holding the pressure/vacuum needed to pass the large-leak test.
Common cause
Parts:purge valve

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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