P2421 — EVAP Vent Valve Stuck Open
The evaporative emission system vent valve does not close on command. The ECU detects that the evap system cannot hold pressure or vacuum because the canister is permanently vented to atmosphere.
General code reference. Confirm the definition and diagnostic procedure for your vehicle's year, model and engine. A stored code alone does not identify a failed part.
Affected components
- Evap vent valve
- Evap canister
Possible causes to check
These are possible checks, not a ranked diagnosis. Follow the vehicle manufacturer's test procedure before replacing parts.
- Vent valve mechanically stuck open
- Dust/debris preventing valve seat
- Carbon or debris buildup preventing free movement
Possible symptoms
- Check engine light on
- Possible smell of fuel near tank or engine bay
- Failed emissions inspection
- Loose-cap warning may appear
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- A drive cycle may be required after repair
Sources
Check each reference's vehicle and model-year scope. General background links do not establish which fault is most likely on your vehicle.
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.