Principles Of Operation
Locks, Latches and Entry Systems
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 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.
Keyless Entry Keypad
The SJB monitors the keyless entry keypad input. When one of the correct codes are entered into the SJB, the SJB carries out the functions associated with the code entered. Based on input from the keypad, the SJB:
- locks all doors.
- unlocks the driver door (with stepped unlock disabled).
- unlocks all doors.
- recalls memory seat/power mirror positions (if equipped).
- enters programming mode.
- enables/disables the autolock feature.
- enables/disables the auto-unlock feature.
Remote Keyless Entry (RKE)
The SJB receives input from a programmed Integrated Keyhead Transmitter (IKT). Based on input from the IKT, the SJB:
- locks all doors.
- unlocks the driver door (with stepped unlock enabled).
- unlocks all doors.
- activates/deactivates the panic alarm.
- arms/disarms the perimeter alarm (if equipped).
- releases the liftgate latch (with power liftgate).
- activates the memory positions (if equipped).
- 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 and the liftgate are closed.
- sounds the horn twice when LOCK is pressed twice within 3 seconds, and any door, or liftgate is open.
- flashes the turn signals once each time LOCK is pressed, and the doors and liftgate are closed.
- if any door is ajar, the turn signals will not flash when LOCK is pressed, until all doors and liftgate are closed.
Field-Effect Transistor (FET) Protection
The SJB utilizes a Field-Effect Transistor (FET) 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 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 protection) and the circuit remains shorted, the FET 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 protected circuit has 3 predefined levels of short circuit tolerance based on the harmful effect of each circuit fault on the FET and the ability of the FET to withstand it. A module lifetime level of fault events is established based upon the durability of the FET. 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), the continuous DTC 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 SJB FET protected output circuits for the handles, locks, latches and entry systems are the liftgate latch release circuit CPL79 (BN/VT) and the keypad illumination circuit CPK28 (WH/GN).