Principles of Operation

Smart Junction Box (SJB)

Principles of Operation

NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).

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 Medium Speed Controller Area Network (MS-CAN). For a detailed list of SJB network inputs and outputs, refer to Principles of Operation in Information Bus. Initial Inspection and Diagnostic Overview

Some SJB parameters are programmable. Two types of programmable parameters are available: vehicle configuration and programmable parameter. For information on programmable parameters, refer to Information Bus.

The SJB utilizes a protective circuit strategy for many of its outputs (for example, the headlamp output circuit). Output loads are monitored by the SJB for excessive current (typically short circuits) and are shut down (voltage or ground provided by the module are turned off) when a fault is detected. A continuous DTC is stored at that time for the fault. The circuit then resets 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 repair procedure is carried out. At the same time, the continuous DTC that was stored on the first failure does not clear by a command to clear the continuous DTCs. The module does not allow this DTC 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 has cleared and the circuit function returns.