Principles of Operation: Notes

WARNING: This page is about a different car, the 2009 Ford Mustang. 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).

When the SJB detects a request for lighting, it turns on the interior lamps by supplying power and ground to the lamps. The request for lighting can be an open door signal from a door ajar switch, an interior lighting on command from the instrument panel dimmer switch or an unlock command from a remote keyless entry (RKE) transmitter.

The SJB monitors input from the door ajar switches and the luggage compartment lid ajar switch. The switches are normally closed when the doors/luggage compartment lid are closed. When the door/luggage compartment lid is opened, the ajar switch opens signalling the SJB. The ajar switches receive a voltage signal from the SJB and each has its own ground circuit.

The instrument panel dimmer switch receives a voltage signal from the SJB. The instrument panel dimmer switch provides variable resistance for backlighting the instrument cluster and a toggle on/off function for the courtesy lamps.

The RKE receiver is contained inside the SJB. When the SJB receives an unlock request from a RKE transmitter, it unlocks the doors and turns on the courtesy lamps.