Diagnostic Aids

Diagnosis of a current DTC U1255 is accomplished through the symptom, scan tool will not communicate with a Class-II device. An intermittent condition is likely to be caused by a short to ground on the serial data link.

When this DTC is set by the Truck body Control (TBC) module, the symptom is most likely to be that the engine does not run. When this DTC is set by the TBC module and the engine runs, this indicates that an ignition feed to either the TBC module/VCM/PCM is open.