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 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 Electrical Diagnosis.. |
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.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Diagnostic System Check performed? | -- | ||
2 |
Can you establish communication with other modules on the class 2 serial data line, such as the PCM? | -- | ||
3 |
Is the resistance measured within the specified range? | OL (Infinite) | ||
4 |
Is the voltage measured within the specified range? | 0 V | ||
5 |
Can you establish communication with the instrument cluster? | -- | ||
6 |
Can you establish communication with the heater A/C control? | -- | ||
7 |
Can you establish communication with the Body Control Module (BCM)? | -- | ||
8 |
Can you establish communication with the Powertrain Control Module (PCM)? | -- | ||
9 |
Is the repair complete? | -- | ||
10 |
Can you establish communication with the EBTCM? | -- | ||
11 | Use J 39200 in order to measure the resistance between the Data Link Connector (DLC) terminal 2 to the 24-way EBTCM connector C1 terminal A1. Is the resistance measured within the specified range? | 0-2 ohms | ||
12 | Replace all terminals or connectors that exhibit signs of poor terminal contact, corrosion, or damaged terminals. Is the repair complete? | -- | -- | |
13 | Repair the short to ground in CKT 1122 or CKT 1132. Is the repair complete? | -- | -- | |
14 | Repair the short to voltage in CKT 1122 or CKT 1132. Is the repair complete? | -- | -- | |
15 | Repair the open in CKT 1122 or CKT 1132 between the Data Link Connector (DLC) terminal 2 and the 24-way EBTCM connector C1 terminal A1. Is the repair complete? | -- | -- | |
16 | Replace the EBTCM. Refer to Electronic Brake and Traction Control Module Replacement . Is the repair complete? | -- | -- | |
17 | Is the malfunction intermittent or is not present at this time? | -- | Go to Diagnostic Aids | -- |
