What causes a U0303 code?

U0303 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 U0303 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with U0303 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.

OBDIY

OBD-II

U0303

Transfer Case Control Module Software Incompatibility

What it means

The software in the transfer case control module is incompatible with other vehicle modules. This can result in 4WD/AWD failures.