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/TCS systems depends on information to and from the PCM for proper operation.
Conditions for Setting the DTC
DTC U1255 sets when 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 stores. |
| • | The ETS/TCS disables. |
| • | The amber ETS/TCS 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 Connector Cell 50 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.
Thoroughly inspect any circuitry that may cause the intermittent complaint for the following conditions:
| • | Backed out terminals |
| • | Improper mating |
| Broken locks |
| Improperly formed or damaged terminals |
| Poor terminal-to-wiring connections |
| • | Physical damage to the wiring harness. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Diagnostic System Check performed? | -- | Go to Diagnostic System Check | |
2 | Use the scan tool in order to attempt to establish communication with the same system on a different vehicle. Can you establish communication on a different vehicle? | -- | Go to Scan Tool Diagnostics | |
3 |
Are there signs of poor terminal contact, evidence of terminal corrosion, or terminal damage? | -- | ||
4 |
Can you establish communication with other modules connected to the serial data line? | -- | ||
5 |
Is the resistance measured within the specified range? | OL (Infinite) | ||
6 |
Is the voltage measured within the specified range? | 0 V | ||
7 |
Can you establish communication with the instrument cluster? | -- | Go to Instrument Cluster System Check | |
8 |
Can you establish communication with the heater A/C control? | -- | Go to Diagnostic System Check | |
9 |
Can you establish communication with the Body Control Module (BCM)? | -- | ||
10 |
Can you establish communication with the Powertrain Control Module? | -- | ||
11 |
Can you establish communication with the EBCM/EBTCM? | -- | ||
12 |
Are there signs of poor terminal contact, evidence of terminal corrosion, or terminal damage? | -- | ||
13 | Use J 39200 in order to measure the resistance between the Data Link Connector (DLC) terminal 2 to the 24-way EBCM/EBTCM connector C1 terminal A1. Is the resistance measured within the specified range? | 0-2 ohms | ||
14 | Replace all terminals or connectors that exhibit signs of poor terminal contact, corrosion, or damaged terminal(s). Is the repair complete? | -- | Go to Diagnostic System Check | -- |
15 | Repair the short to ground in CKT 1122 or CKT 1132. Is the repair complete? | -- | Go to Diagnostic System Check | -- |
16 | Repair the short to voltage in CKT 1122 or CKT 1132. Is the repair complete? | -- | Go to Diagnostic System Check | -- |
17 | Repair the open in CKT 1122 or CKT 1132 between the Data Link Connector (DLC) terminal 2 and the 24-way EBCM/EBTCM connector C1 terminal A1. Is the repair complete? | -- | Go to Diagnostic System Check | -- |
18 | Replace the EBCM/EBTCM. Is the repair complete? | -- | Go to Diagnostic System Check | -- |
19 | Was the Powertrain OBD System Check performed? | -- | -- | |
20 | The malfunction is intermittent or is not present at this time. Is the repair complete? | -- | Go to Diagnostic Aids | -- |
