Principles of Operation

Instrument Cluster and Panel Illumination

Principles of Operation

NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).

Dimmable Backlighting

When the parking lamps are on, the SJB monitors the input from the instrument panel dimmer switch. The SJB sends a pulse-width modulated voltage to the hardwired dimmable components based on input received from the instrument panel dimmer switch. The SJB also sends a message over the Controller Area Network (CAN) to the Audio Control Module (ACM), and the Instrument Cluster (IC) to indicate the backlighting intensity level.

The ACM and IC default to full nighttime brightness if they do not receive the illumination message.

Fixed Backlighting

When the accessory delay relay is energized, switched voltage is supplied to the non-dimmable components and switches. The window control switches and the door lock control switches are the only non-dimmable components.

Field-Effect Transistor (FET) Protection

The SJB utilizes a Field-Effect Transistor (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 can not 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 DTCs 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 instrument panel illumination system are for the LED backlighting output circuit.