Principles of Operation

PRINCIPLES OF OPERATION

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

The SJB receives inputs and delivers outputs to many of the electronically controlled features of the vehicle. The SJB constantly monitors the system under its control and reports a concern in the form of a DTC.

Power Locks
The SJB monitors the door lock control switches. When the SJB receives an unlock/lock command from either door lock control switch, the SJB energizes a relay (internal to the SJB) to supply the correct power and grounds for the door lock actuators.

Liftgate and Liftgate Glass Release
The liftgate release operates the liftgate latch electronically. When the release switch is pushed, the switch is closed, indicating to the SJB to release the liftgate latch.

The SJB monitors the liftgate release switch and the liftgate glass release switch. The doors must be unlocked electronically in order for the SJB to release the liftgate latch or the liftgate glass latch. When this condition is met and the SJB receives a request from the liftgate release switch or the liftgate glass release switch, the SJB provides power to the corresponding latch.

Keyless Entry Keypad
The SJB monitors the keyless entry keypad input. When the correct codes are entered into the SJB, the SJB carries out functions associated with the code entered. Based on input from the keypad, the SJB:
- Locks all doors
- Unlocks the driver door
- Unlocks all doors
- Enters programming mode
- Enables/disables the autolock feature
- Enables/disables the auto-unlock feature
- Releases the liftgate glass

Remote Keyless Entry (RKE)
The SJB receives input from programmed integrated keyhead transmitters (IKTs). Based on input from the IKT, the SJB:
- Locks all doors
- Unlocks the driver door
- Unlocks all doors
- Releases the liftgate glass
- Activates/deactivates the panic alarm
- Turns the interior lamps on (when unlocking) and off (when locking), provided the defeat switch on the dimmer switch is not active
- Sounds the horn once when LOCK is pressed twice within 3 seconds, and the doors are closed
- Sounds the horn twice when LOCK is pressed twice within 3 seconds, and any door is open

Field-Effect Transistor (FET) Protection
The SJB utilizes a 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 that time for the fault. The circuit will then reset 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 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.

Each circuit has three 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 handles, locks, latches and entry systems are the liftgate lock actuator circuit CPL10 (GN/WH) and the keypad illumination circuit CPK28 (WH/GN).