What causes a U0789 code?

U0789 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 U0789 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with U0789 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

U0789

Network/CAN bus communication code U0789

What it means

Lost Communication With AC-DC Converter Control Module B. Communication is severed between the network and the secondary power conversion module.