P0455 on a 2016 Mazda Cx 5
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 Mazda Cx 5
Ranked from 507 NHTSA owner complaints filed for this vehicle.
- 1
Damaged or melted fuel filler neck/pipe
High severityA filler pipe melting and causing a fire is exactly the scale of physical damage that produces a large, easily-detected EVAP leak.
Reported in 1 NHTSA complaintParts:fuel filler neck - 2
Fuel system defect under active NHTSA recall (campaign 16V064000)
Medium severityThe manufacturer-acknowledged fuel-system recall on this vehicle is consistent with a large vapor/fuel leak path that would fail the EVAP monitor's large-leak test.
Reported in 1 NHTSA complaint - 3
Vehicle fire after a fuel-system malfunction (water in fuel, sputtering, then combustion while parked)
High severityA reported fuel-system failure that ended with the parked vehicle bursting into flames indicates a large uncontrolled fuel/vapor leak.
Reported in 1 NHTSA complaint - 4
Missing, loose, or badly damaged gas cap
Low severityThe most common large-leak cause on any vehicle; a cap that isn't sealing at all produces an obvious large-leak failure.
Common causeParts:fuel cap - 5
Cracked or disconnected EVAP line
Medium severityA fully separated or split EVAP hose creates a large leak path rather than a small one.
Common causeParts:EVAP line - 6
Purge or vent valve stuck open
Medium severityA valve unable to close at all prevents the system from holding any pressure/vacuum during the monitor's test.
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.
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