Circuit Description
The class 2 serial data line allows all of the modules on the line to transmit information to each other as needed. Each module is assigned an ID. All of the information sent out on the line is assigned a priority by which it is received. When the ignition is turned ON, each module begins to send and receive information. Each module on the class 2 serial data line knows what information the module needs to send out and what information the module should be receiving. What the modules do not know is which module is supposed to send the information. This information is only learned after the module has received the information needed along with the ID of the module that sent the information. This information is then remembered until the ignition switch is turned OFF.
Conditions for Running the DTC
The ABS conditions and the braking conditions are normal.
Conditions for Setting the DTC
The PCM does not receive any messages from the EBCM.
Action Taken When the DTC Sets
| • | The EBCM disables the ETS for the duration of the ignition cycle. |
| • | The TRAC OFF indicator turns ON. |
| • | The ABS remains functional. |
Conditions for Clearing the DTC
| • | The condition for setting the DTC is no longer present and the scan tool Clear DTCs function is used. |
| • | The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles. |
Diagnostic Aids
The following are possible causes of this DTC:
| • | The EBCM has a class 2 serial data transmit malfunction. |
| • | The PCM has a class 2 serial data receiver malfunction. |
| • | The class 2 serial data line has an extremely high amount of traffic. |
| • | Loose or corroded EBCM ground or PCM ground. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step checks to see if the PCM set DTC U1000 or U1255.
-
This step checks to see if the IPC or SDM set DTC U1040.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the ABS Diagnostic System Check? | -- | Go to Step 2 | |
Does the scan tool display DTC U1000 or U1255? | -- | Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications | Go to Step 3 | |
Does the scan tool display DTC U1040 for either module? | -- | Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications | Go to Step 4 | |
4 | Inspect the ground G112, making sure the ground is clean and torqued to the proper specification. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 7 | Go to Step 5 |
5 |
Does the DTC reset? | -- | Go to Step 6 | Go to Diagnostic Aids |
6 | Replace the EBCM. Refer to Electronic Brake Control Module Replacement . Did you complete the replacement? | -- | Go to Step 7 | -- |
7 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
