Principles of Operation

PRINCIPLES OF OPERATION

NOTE: The smart junction box (SJB) is also known as the generic electronic module (GEM).

The SJB monitors the multifunction switch position by sending multiple voltage reference signals to the multifunction switch. When the multifunction switch is in the LH or RH TURN positions, or the hazard lamp switch is engaged, that input signal is routed to ground.

When the SJB receives an input from the multifunction switch indicating a request for a turn signal or hazard lamps, the SJB cycles the voltage on and off approximately 80 times per minute to the appropriate turn lamps.

If a front or rear turn bulb is inoperative, the SJB cycles the voltage on and off approximately 160 times per minute for bulb outage indication.

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 the time of the fault. The circuit then resets 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 cannot be cleared by a command to clear the continuous DTCs. The module does 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 clears and the circuit function returns.

Each circuit has 3 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. These DTCs cannot be cleared and the module must be replaced.

The SJB FET protected output circuits for the turn lamp system are for the LH front turn lamp output, the RH front turn lamp output, the LH rear turn lamp output (Mountaineer only) and the RH rear turn lamp output (Mountaineer only) circuits. For Explorer and Explorer Sport Trac, the rear turn lamps utilize the stoplamp circuitry.