What causes a P0781 code?

P0781 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 P0781 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P0781 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

P0781

P0781: 1-2 Shift Malfunction Transmission Selection

What it means

The Transmission Control Module (TCM) has detected a failure during the 1-2 gear upshift or downshift sequence, indicating a mechanical or hydraulic synchronization error.