P0442 on a 2020 Ram 1500 Classic

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 2020 Ram 1500 Classic

Ranked from 613 NHTSA owner complaints filed for this vehicle.

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1
Faulty fuel filler neck / rollover check valve (5th-gen Ram TSB)
Medium severity
Multiple complaints describe fuel splashing back and repeated pump shutoffs while refueling due to a stuck rollover valve/pressure buildup in the filler neck — a documented issue on 5th-generation Ram trucks with an active TSB.
Reported in 4 NHTSA complaints
Parts:fuel filler neck
2
Fuel-saturated or failed EVAP charcoal canister
Medium severity
Several of the same complaints report the canister/purge system being soaked with liquid fuel backing up from the filler neck, and dealers replacing the canister as the fix.
Reported in 3 NHTSA complaints
Parts:EVAP charcoal canister
3
Purge valve leaking or stuck open
Low severity
One complaint describes fuel leaking into the purge valve and dumping into the intake manifold during refueling, consistent with a compromised purge valve seal.
Reported in 1 NHTSA complaint
Parts:purge valve
4
Loose, cross-threaded, or worn gas cap
Low severity
The single most common EVAP leak source generally; a cap that doesn't seal or click fully lets the system fail its leak test. Try a new cap first.
Common cause
Parts:gas cap
5
Cracked or brittle EVAP vapor line/hose
Low severity
Age-hardened rubber lines under the vehicle crack and leak vapor; smoke-test the EVAP system to pinpoint the leak location.
Common cause
Parts:EVAP hose
6
Vent valve (canister vent solenoid) stuck open or leaking
Low severity
The vent valve must seal the system for the leak test to pass; a stuck-open valve produces a constant small/large leak code depending on how it fails.
Common cause
Parts:vent valve
7
Rusted or corroded fuel filler neck (general aging, distinct from the rollover-valve TSB)
Medium severity
Corrosion or physical damage to the filler neck, common in road-salt regions, can create a large EVAP leak path on its own; inspect the neck and hose clamps.
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