Principles of Operation
Locks, Latches and Entry Systems
Principles of Operation
Power Locks
NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).
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 to supply the correct power and grounds for the door lock actuators.
Liftgate Release
The liftgate release switch operates the liftgate latch electronically. When the switch is pressed, the SJB processes the input and releases the liftgate latch.
The doors must be unlocked electronically in order for the SJB to release the liftgate latch. When this condition is met and the SJB receives the input from the liftgate release switch, the SJB provides power to the latch release motor.
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.
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.
- activates/deactivates the panic alarm.
- arms/disarms the perimeter alarm (if equipped).
- if equipped, issues a command over the communication network to the Liftgate/Trunk Module (LTM) to open the power liftgate.
- if equipped, activates the memory positions.
- 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
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 protection strategy is used to prevent module damage in the event of excessive current flow
The Smart Junction Box (SJB) utilizes each FET to switch its main outputs (for example, the headlamp output circuit) on or off. An FET protective circuit strategy is used for many of these outputs. Each FET is monitored for excessive current (typically short circuits) and is shut down (turns off the voltage or ground provided by the module) when a fault event is detected. A continuous DTC for the SJB output is stored at the fault event and a cumulative counter is started.
When the demand for the output is no longer present, the SJB resets the FET circuit protection. The next time the output is requested on, the SJB activates the output again. For each cycle that the SJB protective strategy detects a circuit fault and shuts down the FET, a counter inside the SJB advances toward a programmed limit.
When the cumulative counter exceeds the programmed limit, the SJB shuts down the output until a repair procedure is carried out. The programmed limit is established based upon the durability of the FET. Each FET protected circuit has 3 thresholds (or stages) which occur at incremental points in this process. Even though first and second threshold DTCs can be cleared, the counter does not reset to zero. This is due to the cumulative effects of the circuit fault on the FET.
When the first and second thresholds are reached the FET is locked in a disabled state and a continuous DTC for the SJB output is stored. In addition, B106E is set in the SJB at the same time. The process for clearing these 2 DTCs is different than for most other CMDTCs. The module does not allow the codes to be cleared or the circuit restored to normal operation until a successful self-test proves that the fault has been repaired and the codes are cleared. Upon a successful on-demand self-test and the clearing of DTC B106E, the circuit function returns. If the counter reaches the third level, 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 circuit for the handles, locks, latches and entry systems is the liftgate lock actuator circuit CPL10 (GN/WH).