Principles Of Operation

Interior Lighting

Principles of Operation

The Smart Junction Box (SJB) supplies voltage to the interior lighting system. The interior lighting system illuminates the courtesy lamp to enhance visibility of the interior. When a vehicle door is ajar and the vehicle speed is less than 15 km/h (9 mph), or the instrument panel dimmer switch is in the DOME LAMP position, the SJB (Smart Junction Box) provides voltage to the courtesy lamp circuit. The SJB (Smart Junction Box) controls all interior lighting functions and timing by monitoring inputs from the door ajar switches, the instrument panel dimmer switch, and vehicle speed.

The instrument panel dimmer switch receives a voltage signal from the SJB (Smart Junction Box). The instrument panel dimmer switch provides variable resistance for backlighting the Instrument Panel Cluster (IPC) and a toggle on/off function for the courtesy lamp.

The Remote Keyless Entry (RKE) receiver is contained inside the SJB (Smart Junction Box). When the SJB (Smart Junction Box) receives an unlock request from a RKE (Remote Keyless Entry) transmitter, it unlocks the doors and turns on the courtesy lamp.

Interior Lamp Arbitrator

The SJB (Smart Junction Box) chooses between the interior lighting, dome defeat, interior lighting delay, illuminated entry, illuminated exit and battery saver to determine which feature has precedence of activating and deactivating the interior lamps.

Ambient Lighting

The Body Control Module B (BCM-B) monitors the door courtesy lighting, courtesy lighting delay and illuminated exit requests. When a door is opened, the BCM-B (Body Control Module B) turns on all 3 zones of the ambient lighting system. Zone 3 (door scuff plate LEDs) are turned off when any door is closed, or the illuminated entry request is detected by the BCM-B (Body Control Module B). The other 2 zones are turned off at the same time as the courtesy lighting by the BCM-B (Body Control Module B) if the key is not activated in the ignition switch. The ambient lighting is reactivated when the ignition is placed in the accessory ON or RUN position.

The color of the LEDs always defaults to the last setting in the memory. There are 125 different color combinations that are achieved by adjusting the 3 primary (red, green and blue) colors.

Field-Effect Transistor (FET) Protection

Field-Effect Transistor (FET) is a type of transistor that when used with module software can be used to monitor and control current flow on module outputs. The FET (Field-Effect Transistor) protection strategy is used to prevent module damage in the event of excessive current flow.

The SJB (Smart Junction Box) utilizes an FET (Field-Effect Transistor) protective circuit strategy for many of its outputs (for example, a 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 event is detected. A continuous DTC is stored at the fault event and a cumulative counter is started.

When the demand for the output is no longer present, the module resets the FET (Field-Effect Transistor) circuit protection to allow the circuit to function. The next time the driver requests a circuit to activate that has been shut down by a previous short (FET (Field-Effect Transistor) protection) and the circuit remains shorted, the FET (Field-Effect Transistor) protection shuts off the circuit again and the cumulative counter advances.

When the excessive circuit load occurs often enough, the module shuts down the output until a repair procedure is carried out. Each FET (Field-Effect Transistor) protected circuit has 3 predefined levels of short circuit tolerance based on the harmful effect of each circuit fault on the FET (Field-Effect Transistor) and the ability of the FET (Field-Effect Transistor) to withstand it. A module lifetime level of fault events is established based upon the durability of the FET (Field-Effect Transistor). If the total tolerance level is determined to be 600 fault events, the 3 predefined levels would be 200, 400 and 600 fault events.

When each tolerance level is reached, 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 operation until a successful self-test proves that the fault has been repaired. After the self-test has successfully completed (no on-demand DTCs present), DTC B106E and the associated continuous DTC (the DTC related to the shorted circuit) automatically clears and the circuit function returns.

When the first or second level is reached, the continuous DTC (associated with the short circuit) sets along with DTC B106E. These DTCs can be cleared using the module on-demand self-test, then the Clear DTC operation on the scan tool (if the on-demand test shows the fault corrected). The module never resets the fault event counter to zero and continues to advance the fault event counter as short circuit fault events occur.

If the number of short circuit fault events reach the third level, then DTCs B106F and B1342 set along with the associated continuous DTC. This DTC cannot be cleared and the module must be replaced.

The BCM-B (Body Control Module B) utilizes a similar strategy.

The SJB (Smart Junction Box) FET (Field-Effect Transistor) protected output circuits for the interior lighting system is the courtesy lamp output circuit.

The BCM-B (Body Control Module B) FET (Field-Effect Transistor) protected output circuits for the interior lighting system are the ambient lighting output circuits.