Antilock Brake System

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 for 7 seconds.

Action Taken When the DTC Sets
^ The EBCM disables the TCS for the duration of the ignition cycle.
^ The TRACTION CONTROL indicator turns ON.
^ The ABS remains functional.

Conditions for Clearing the DTC
^ The condition for the DTC is no longer present (the DTC is not current) and you used the scan tool Clear DTC function.
^ The condition for the DTC is no Longer present (the DTC is not current) and you used the On-Board Diagnostics Clear DTC function.
^ The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Diagnostic Aids
Possible causes of this DTC are the following conditions:
^ The EBCM has a class 2 serial data transmit fault.
^ The PCM has a class 2 serial data receiver fault.
^ The class 2 serial data line has an extremely high amount of traffic.
^ Loose or corroded EBCM ground or PCM ground.

Test Description
The number below refers to the step numbers on the diagnostic table.
2. This step checks to see if the PCM, IPC, or SDM has set DTC U1040.