Powertrain, generic (extended)

P2421 EVAP System Vent Valve Stuck Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

The vent valve closes off the evaporative system, letting a leak test hold pressure or vacuum. P2421 says the valve stays open when the controller has commanded it shut; the test then fails to seal, much like a gross leak. Which valve is meant depends on the design. GM's Volt with a sealed tank and leak check pump (16OBDG01) reports a stuck-open diurnal control valve as one result of its pump test sequence, Type B. Porsche applies P242100 on plug-in Cayenne and Panamera models to the tank isolation valve; carbon dust from the canister can spoil its sealing membrane, and the guided troubleshooting was revised. CARB requires the evaporative system and its valves to be monitored. Driving is unaffected, but the leak test stays incomplete.

Likely causes

Valve seat or membrane contaminated by charcoal dust or dirt
Vent or tank isolation valve mechanically stuck open
Disintegrating charcoal canister shedding particles

Symptoms

  • Check engine light, no driveability change
  • EVAP readiness not set, leak codes possible

Repair estimate

DifficultyMediumDIY possible
Parts and labour€60–600
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

evap vent valveevap canister

Related codes

P2422P0455P0442P0446P0496

References: gsi.ext.gm.com, static.nhtsa.gov, static.nhtsa.gov, law.cornell.edu.