P2421EVAP System Vent Valve Stuck Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- Check engine light, no driveability change
- EVAP readiness not set, leak codes possible
- Likely causes
- LikelyValve seat or membrane contaminated by charcoal dust or dirt
- PossibleVent or tank isolation valve mechanically stuck open
- RareDisintegrating charcoal canister shedding particles
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €60 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.