Principles of Operation

PRINCIPLES OF OPERATION

The smart junction box (SJB) monitors the headlamp switch position by sending voltage reference signals on multiple circuits to the headlamp switch. At any given time, one of the signal circuits is routed to ground. If the SJB does not detect any of the inputs to the headlamp switch is active (routed to ground) for 5 seconds, the SJB turns on the exterior lights and keeps them on for 10 minutes after the ignition switch is turned off (or 10 minutes from the time the SJB does not detect any headlamp switch input if the ignition switch was already off). If the SJB detects multiple circuits short to ground, the SJB implements a planned strategy depending on the multiple inputs received. If either of these situations occur, the SJB should NOT be ruled immediately as being at fault. This is normal behavior of the SJB design as it has detected a fault with the inputs from the headlamp switch.

The SJB also monitors the multifunction switch for a flash-to-pass or high beam request. There are 2 voltage reference circuits which monitor this. When the multifunction switch is in the FLASH-TO-PASS or HIGH BEAM position, the voltage signal is routed to ground.

NOTE: The flash-to-pass feature does not require any input from the headlamp switch.

When the SJB receives an input requesting the headlamps on, the SJB supplies voltage to the low beams. If the low beams are on and the SJB receives a request for high beams (or just a flash-to-pass request), the SJB energizes an internal relay which routes voltage to the headlamps.

Field-Effect Transistor (FET) Protection
The SJB utilizes a FET 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 DTC is stored at that time for the fault. The circuit will then reset after a customer demand of the function (switching the component on, 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 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 operation 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.

Each circuit has three predefined levels of short circuit tolerance established in the module based on each circuits' capability. When the first or second level is reached, the continuous DTC associated with the circuit sets along with DTC B106E. These DTCs may be cleared using the Clear DTC operation on the scan tool as long as the fault itself has been corrected. If any of the circuits are shorted past the third level, then B106F and B1342 set along with the associated continuous DTC. This DTC cannot be cleared and the module must be replaced.

The SJB FET protected output circuits for the headlamp system are for the LH low beam output and the RH low beam output circuits.