U1255 Generic Loss of Communication

Page 1 Of 2:

Page 2 Of 2:

CIRCUIT DESCRIPTION
The serial data communications circuits (CKT 1122, CKT1132 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 PCM for proper operation.

CONDITIONS FOR SETTING THE DTC
DTC U1255 sets when the vehicle speed is greater that 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 massage for at least 10 seconds.

ACTION TAKEN WHEN THE DTC SETS
- A malfunction Diagnostic Trouble Code (DTC) stores.
- The ETS disables.
- The amber ETS OFF indicator (TRAC OFF) turns on.

The ABS remains functional. No action towards the electronic brake control relay and ABS warning indicator is taken.

CONDITIONS FOR CLEARING THE DTC
- The condition responsible for setting the DTC no longer exits and the Scan Tool Clear DTCs function is used.
- 100 drive cycles pass with no DTCs detected.

DIAGNOSTIC AIDS
When DTC U1255 is current (malfunction in CKT 1122, CKT 1132 and CKT 1049), no communication can be established with the Powertrain Control Module (PCM). When the malfunction is present, DTC U1255 stores in system memory.

Before beginning this DTC table, perform a Powertrain OBD System Check in order to eliminate the PCM as the possible source of the malfunction.

The following conditions may cause an intermittent malfunction:
- A poor connection
- Rubbed-through wire insulation
- A broken wire inside the insulation within the
Serial Data Line. Refer to "Data Link Communications System Check" in Diagrams.
Use the enhanced diagnostic function of the Scan Tool in order to measure the frequency of the malfunction. Refer to the Scan Tool manual for the procedure.
- ABS Indicator Off No DTC Set