U1255-Class 2 Communications Malfunction - ABS

DTC U1255 (1 Of 3):

DTC U1255 (2 Of 3):

DTC U1255 (3 Of 3):

CIRCUIT DESCRIPTION
The serial data communications circuits (CKT 1122, CKT 1132 and CKT 1049) is used to transmit messages from one electronic control module to another when interface is necessary between systems. The ABS/ETS systems depends on information to and from the Powertrain Control Module (PCM) for proper operation.

CONDITIONS FOR SETTING THE DTC
DTC U1255 will set when the vehicle speed is greater than 4.8 km/h (3 mph) and there is a malfunction on the serial data circuit, or if the PCM has not broadcasted a serial message for at least 10 seconds.

ACTION TAKEN WHEN THE DTC SETS
A malfunction DTC is stored, ETS is disabled. The amber ETS off indicator (TRAC OFE3 is turned on. The ABS remains functional. No action towards the electronic brake control relay and ABS warning indicator is taken.

CONDITIONS FOR CLEARING DTC
Condition for DTC is no longer present and the scan tool (CLEAR DTCs) function is used, or 100 drive cycles have passed with no DTC(s) detected.

DIAGNOSTIC AIDS
When DTC U1255 is current (malfunction in CKT 1122, CKT 1132 and CKT 1049), no communication can be established with the PCM. When the malfunction is present, DTC U1255 will be stored in system memory. Before beginning this DTC table a Powertrain OBD System Check should be performed to eliminate the PCM as the possible source of the malfunction. An intermittent malfunction may be caused by a poor connection, rubbed-through wire insulation, or a wire that is broken inside the insulation within the Serial Data Line. The frequency of the malfunction can be checked by using the enhanced diagnostic function of the Scan Tool. Any circuitry that is suspected of causing the intermittent complaint should be thoroughly checked for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wiring connections, or physical damage to the wiring harness.