Trailer Lamps

PRINCIPLES OF OPERATION

The smart junction box (SJB) monitors the base vehicle lighting systems. When the turn or stoplamps are illuminated, the SJB provides voltage to the trailer turn/stoplamps at the same time. The parking lamp relay for the vehicle also provides voltage to the trailer parking lamps when energized.

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.