What causes a U0843 code?

U0843 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 U0843 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with U0843 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

U0843

Network/CAN bus communication code U0843

What it means

Lost communication with the Transmission Control Module (TCM). The engine ECU is unable to sync with the transmission for shifting or torque management.