Headlamp: Description and Operation

HEADLAMPS

Principles of Operation

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

Voltage is supplied at all times by the smart junction box (SJB) to the headlamp switch. When the headlamp switch is placed in the HEADLAMPS ON position, voltage is routed to the multifunction switch. The multifunction switch then routes the voltage to the SJB, which routes voltage to the headlamps. The SJB also supplies voltage to the multifunction switch at all times. When the flash-to-pass feature is engaged, voltage is routed to the SJB, which routes the voltage to the high beams.
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 DTC is stored at that time for the fault. The circuit will the 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 repair 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.