P0442 on a 2016 Mercedes Benz C Class Phev

P0442 means the EVAP system could not hold pressure or vacuum during a leak test, but the leak is small.

Not your vehicle? See general P0442 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 or loose fuel/vapor line and hose clamps (recall-related fuel leak)
High severity
This is by far the dominant complaint in this population: a cracked low-pressure fuel hose or a compression clamp that loosens in cold weather leaks fuel/vapor near the tank and engine bay, producing the gas smell reported by dozens of owners and covered under an extended-warranty campaign.
Reported in 12 NHTSA complaints
Parts:fuel line fuel line clamp
2
EVAP vent valve failure
Medium severity
One owner's dealer specifically diagnosed a failed EVAP vent valve accompanied by a persistent gasoline smell and check-engine light.
Reported in 1 NHTSA complaint
Parts:vent valve
3
Loose, damaged, or worn gas cap
Low severity
Still the simplest and most common cause of a small EVAP leak code; verify the cap seats and clicks fully.
Common cause
Parts:fuel filler cap
4
Purge valve stuck or leaking
Medium severity
A purge solenoid that doesn't seal lets vapor bleed past during the EVAP self-test.
Common cause
Parts:purge valve
5
Charcoal canister cracked or fuel-saturated
Medium severity
A damaged or liquid-fuel-soaked canister cannot hold vacuum/pressure during the leak-check monitor.
Common cause
Parts:charcoal canister
6
Corroded fuel filler neck
Low severity
Rust-through on the filler neck creates a persistent small vapor leak path.
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. P0442 on your car still needs shop confirmation before any repair.

Common symptoms

Check engine light
Fuel smell near vehicle
Usually drives normally
Hard start after fueling in some cases

What to check before replacing parts

Tighten and inspect the gas cap

Look for: A cap that doesn't click to full tightness, has a visibly cracked or flattened seal, or is simply missing is the single most common cause of a small EVAP leak — rule it out first.

Smoke-test the EVAP system

Look for: Because this is a small leak, expect only a thin wisp of smoke or a faint hiss at one spot (a hose, seam, or valve) rather than an obvious cloud — look closely and take your time.

Check purge valve sealing

Look for: A purge valve that doesn't hold vacuum when commanded closed lets a small amount of air bleed through, which the system reads as a leak during its self-test.

Inspect hoses near the tank and engine bay

Look for: Look for small cracks, soft/collapsed spots, or a hose that has pulled loose slightly at a fitting — any of these can leak just enough to trip a small-leak code without an obvious fuel smell.

Verify vent valve operation

Look for: A vent valve that doesn't seal fully when commanded closed prevents the system from holding vacuum during its self-test, which reads as a small leak even with no physical leak in the hoses.

Rather have a pro handle it? Find a vetted local mechanic.

Matching symptoms

Check Engine Light