Principles of Operation

WARNING: This page is about a different car, the 2009 Mercury Milan, 2009 Lincoln MKZ, and 2009 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.

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

The 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 detects any concern with the inputs from the headlamp switch for 5 seconds, the SJB may turn on the exterior lights and keep them on for 10 minutes after the ignition switch is turned off (or 10 minutes from the time the SJB detects any headlamp switch input concern if the ignition switch was already off).

If the SJB detects a concern with the headlamp switch inputs, the SJB implements a planned strategy depending on the inputs received. If this situation occurs, 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 light sensor with a voltage reference signal. The light sensor input to the SJB varies with the ambient light conditions.

When the SJB receives an input from the headlamp switch indicating a request for the AUTOLAMPS, the SJB monitors the light sensor for the ambient light condition. If the SJB determines the ambient light level is dark, the SJB supplies voltage to the exterior lamps.

Vehicles equipped with AUTOLAMPS also have a feature that turns on the exterior lamps when the windshield wipers are on. When the SJB detects a ground signal from the windshield wiper motor, the SJB turns the exterior lamps on. For additional information, refer to WIPERS AND WASHERS .