P0455 on a 2016 Mercedes Benz C Class Phev

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 Mercedes Benz C Class Phev

Ranked from 317 NHTSA owner complaints filed for this vehicle.

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1
Cracked/loose fuel supply line or hose clamp (recall-related large fuel leak)
High severity
The dominant fault in this data set - a cracked low-pressure fuel hose or a compression clamp that loosens when cold produces a strong, continuous gas smell in the cabin, large enough to register as a large EVAP/fuel-system leak; the subject of an extended fuel-line warranty campaign.
Reported in 12 NHTSA complaints
Parts:fuel line fuel line clamp
2
EVAP vent valve stuck open
Medium severity
An owner's dealer diagnosed a failed vent valve alongside a persistent fuel odor - a stuck-open vent valve reads as a large leak on the monitor.
Reported in 1 NHTSA complaint
Parts:vent valve
3
Missing or badly damaged gas cap
Low severity
A cap left off or with a torn seal is the classic large-leak trigger and the first thing to rule out.
Common cause
Parts:fuel filler cap
4
Cracked or disconnected EVAP line
Medium severity
A fully split or detached vapor hose between tank and canister opens a large leak path.
Common cause
Parts:EVAP hose/line
5
Charcoal canister damage
Medium severity
Physical damage or corrosion of the canister housing can open a large enough leak to fail the monitor.
Common cause
Parts:charcoal canister
6
Rusted-through fuel filler neck
Low severity
Severe corrosion perforating the filler neck is a common large-leak source on older vehicles.
Common cause
Parts: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.

Matching symptoms

Check Engine Light