The P2421 code indicates that the evaporative emission control (EVAP) system vent valve is stuck in the open position. This valve is normally closed during the EVAP system self-test to seal the system and check for fuel vapor leaks. When it cannot close, the system cannot build or hold pressure, triggering the code.
The valve solenoid or internal mechanism has failed mechanically or electrically, preventing it from sealing shut when commanded.
Dirt, mud, rust, or spider webs can physically prevent the valve pintle from closing properly, which is very common since the valve is often exposed to the atmosphere under the vehicle.
Corroded, broken, or disconnected wiring and terminals can prevent the electrical signal from reaching the valve, leaving it in the default open state.
Degraded charcoal from a failing canister can migrate into the vent valve, physically jamming it open.
The engine computer fails to command the valve closed, though this is an extremely rare cause of this code.
Yes, this code rarely affects engine performance or drivability. However, it will prevent the EVAP system from testing properly and will result in a failed emissions test.
No, replacing the powertrain control module is almost never the correct fix for this code. The issue is almost always a physical failure or blockage in the vent valve itself, or a wiring problem.
Because the vent valve vents the fuel tank to the atmosphere, its opening is exposed. Dirt, road grime, rust, and spider webs frequently enter the valve and physically jam it open.
No, a loose gas cap typically causes a general EVAP leak code. P2421 specifically means the system detects the vent valve cannot close mechanically or electrically, which a gas cap fix will not resolve.