P2421
Evaporative Emission System Vent Valve Stuck Open
- Severity
- Low
- Driving
- Drivable — book it in
The evaporative emission vent valve is stuck open. This valve normally sits open, letting the charcoal canister breathe fresh air, and closes only to seal the system for a leak test. Stuck open, it cannot seal - so the module reports that the system will not hold vacuum, and the leak test never passes. It causes no driving problem at all.
Possible causes
- CommonDebris or corrosion holding the valve open
- CommonFailed valve solenoid
- CommonCharcoal from a saturated canister jamming the valve
- PossibleWater that has entered and corroded the valve internals
- PossibleWiring or connector fault so the valve is never commanded shut
What you might notice
- Check engine light on
- Failed emissions test
- Occasionally a smell of fuel
- Usually nothing else - EVAP faults rarely affect how the car drives
What to check, in order
- Inspect the connector and its wiring before condemning the component. Everything in this system lives under the vehicle in the path of road salt and spray, and a corroded connector produces these codes far more often than a failed part does.
- Command the valve closed with a scan tool and check whether the system then holds vacuum. That separates a stuck valve from a leak elsewhere.
- Check the canister for charcoal breakdown. A collapsing canister sends charcoal dust downstream and jams the vent valve, and replacing the valve alone lets it happen again.
- Look for a large EVAP leak code stored alongside. The vent valve stuck open is one of the most common reasons for one.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx