What causes a P2421 code?

P2421 can be triggered by several issues — see the verified probable causes and step-by-step diagnostics shared by mechanics and owners on OBDIY.

Can I drive with a P2421 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P2421 active.

Follow the step-by-step diagnostic on this page, then read the verified fixes contributed by other Heavy Truck owners — the answer marked "Verified Cause" worked for the original poster.

OBD-II

P2421

Evaporative Emission System Vent Control Valve Stuck Open

What it means

Indicates the powertrain control module detected that the evaporative emission (EVAP) vent valve or solenoid is stuck in the open position. While rare on heavy-duty diesel engines, this code occasionally triggers on medium-duty or vocational chassis using specialized fuel-management hardware.