P0442 on a 2018 Subaru Outback
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 2018 Subaru Outback
Ranked from 805 NHTSA owner complaints filed for this vehicle.
- 1
EVAP purge or vent valve malfunction
Medium severityAn owner found the tank not venting properly, high pressure at the cap, and slow fill - classic signs of a stuck purge/vent valve disrupting the EVAP monitor.
Reported in 1 NHTSA complaint - 2
Rodent-damaged EVAP or fuel vapor line
Medium severityAn owner documented a rodent chewing through fuel/vapor lines and harnesses, a known issue on this generation's soy-based line insulation.
Reported in 1 NHTSA complaintParts:EVAP hose/line - 3
Loose, damaged, or missing gas cap
Low severityThe single most common trigger for a small EVAP leak code; the cap fails to seal and lets vapor escape.
Common causeParts:gas cap - 4
Cracked or brittle EVAP hose from age
Low severityRubber EVAP lines harden and crack over time, producing a small, steady vapor leak.
Common causeParts:EVAP hose - 5
Charcoal canister crack or saturation
Medium severityA cracked canister housing or an over-saturated canister (from repeated overfilling) leaks vapor instead of containing it.
Common causeParts:charcoal canister - 6
Rusted or damaged fuel filler neck
Low severityCorrosion or physical damage to the filler neck breaks the seal path to the cap, causing a small detectable leak.
Common causeParts: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.
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