Body Control Module: Description and Operation

SMART JUNCTION BOX (SJB)

Principles of Operation

The SJB is a multifunction module that controls many of the vehicle systems. Several SJB functions utilize hardwired inputs and/or outputs. The SJB controls the following hardwired functions, using the corresponding inputs and outputs:





In addition, the SJB is involved in other vehicle systems through communication over the CAN. For a detailed list of SJB network inputs and outputs, refer to Communications Network.
Some SJB parameters are programmable. Two types of programmable parameters are available: vehicle configuration and customer preference. For additional information on programmable parameters, refer to Programmable Module Installation.
The SJB utilizes a protective circuit strategy for many of its outputs (for example, the headlamp output circuit). Output loads (current level) are monitored for excessive current (typically short circuits) and are shut down (turns off the voltage or ground provided by the module) when a fault is detected. A continuous diagnostic trouble code (DTC) is stored at that time for the fault. The circuit will then reset after an ignition cycle or customer demand of the function (switching the component on, 30-minute battery saver being energized). When an excessive circuit load occurs several times, the module shuts down the output until a service procedure is performed. At the same time, the continuous DTC that was stored on the first failure will not clear by a command to clear the continuous DTCs. The module will not allow this code to be cleared or the circuit restored to normal until a successful on-demand self-test proves that the fault has been repaired. After the on-demand self-test has successfully completed (no on-demand DTCs present), the continuous DTC will have been cleared and the circuit function will return.