What causes a U3406 code?

U3406 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 U3406 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with U3406 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

U3406

Manufacturer-specific network code U3406

What it means

Communication fault with the Trailer Interface Module. The truck cannot negotiate light or brake signals over the J1939-trailer link.