Body Control Module: Description and Operation
General
The GEM (generic electronic module) centralises the control of several body systems, reducing electrical complexity and increasing overall system reliability. The GEM (generic electronic module) controls the routines of the following systems:
^ Anti-theft alarm system
^ Car/Key Memory
^ Central locking system and child safety lock
^ Door mirror control
^ Headlamp wipers and washers
^ Interior lighting
^ Load disconnection
^ Roof opening panel
^ Approach Lamps
^ Window regulators
^ Windshield wipers and washers.
The vehicle type, equipment configuration and market specific features are specified to the GEM (generic electronic module) by means of coding data via the diagnostics interface.
Load switching circuits for currents <10 A consist of semiconductor switches within the GEM (generic electronic module). The load switching circuits for the headlamp and windshield wipers are subjected to a greater degree of loading (number of operating cycles and current loading), so the switching is performed outside the GEM (generic electronic module) by relays.
Car/Key Memory
The car memory contains vehicle function settings that can be changed to suit market and customer preferences. In some markets, some of the functions in the vehicle memory are blanked out due to marketing and statutory requirements. Where available, the settings can be changed using T4.
The key memory is based on the vehicle memory, and contains function settings that can be personalised to an individual driver. Different drivers are recognised indirectly through the remote control transmitter in the key. Up to four different keys can be recognised by the GEM (generic electronic module). The key memory settings can be changed using T4.
The GEM (generic electronic module) broadcasts driver recognition on the P bus and the K bus to the following control modules, which also contain personalised key memory settings:
^ Driver door module, for memorised door mirror settings
^ Memory control module, for memorised driver's seat and steering column settings
^ Radio, for memorised tone, audio source and station settings.
The driver recognition messages contain the key number, the button pressed on the remote control and whether the key is valid or not. The key number is contained in the unlock transmission of the remote control keys, so personalised settings are only recalled after the vehicle has been unlocked with the remote control of one of the key numbers stored in the key memory. If the vehicle is unlocked with the key in the driver's door lock, the GEM (generic electronic module) identifies the key as invalid and control modules with personalised settings recall the last used setting. The GEM (generic electronic module) outputs the driver recognition message when it detects:
^ An 'unlock' command from a remote control (the signal is sent immediately so that the correct positions for seat, door mirrors and steering column can be set)
^ Any other actuation by remote control (when the remote control 'lock' command is detected, seat motion to a memorised position is stopped)
^ Operation of the central locking system by other than a remote control
^ A change of state of the ignition switch
^ A driver recognition enquiry from another control module.
The seat and steering column memories are coded with an automatic movement option for the driver's seat, door mirrors and steering column. The options are:
^ No automatic setting
^ Automatically setting the positions in response to the remote control 'unlock' command
^ Automatically setting the positions in response to the remote control 'unlock' command and opening of the driver's door.
Automatic movement of the seat can be stopped by pressing the remote control 'lock' button or any of the seat adjustment or memory switches. Automatic movement can be restarted by pressing the remote control 'lock' button again. Pressing the 'unlock' buttons (for selective central locking) and 'unlocking the boot' does not stop automatic seat movement.
Storage of personalised settings is automatically updated for each setting change provided a valid remote control key has been detected (interruption of the automatic recall movement of the driver seat, door mirrors and steering column is not interpreted as a setting change). The last setting for the recognized driver is automatically stored in the key memory area of the corresponding control module. If no valid remote control key has been detected, setting changes are stored in a recall memory for retrieval when an invalid key is detected.
The following table contains the car and key memory functions that can be changed (depending on market) using T4.
Load Disconnection
The GEM (generic electronic module) supplies various electrical loads on the vehicle, such as the glove compartment lamp, reading lamps, luggage compartment lamps, etc., that can be switched on and remain on when the vehicle is parked. A central load disconnection feature in the GEM (generic electronic module) ensures the battery is not discharged in the event these loads are switched on continuously. The trigger time after the ignition is switched off is 16 minutes and is independent of the sleep mode timer.
The GEM (generic electronic module) disconnects the following loads while the engine cranks, to maximise the available power from the battery:
^ Wipers
^ Washer pump
^ Headlamp cleaning
^ Window regulators
^ Roof opening panel.
If the one-touch function of a window or the roof opening panel is active before the load disconnection, the function is not continued when engine cranking stops.
Sleep Mode
To conserve power, the entire GEM (generic electronic module) goes into a 'sleep' mode 16 minutes after signal activity ceases and the ignition is switched off. The typical current consumption of the GEM (generic electronic module) in sleep mode is 1.25 mA. In the sleep mode the GEM (generic electronic module) is in a limited operational mode from which it can be awakened by certain relevant wake-up signals. After being awakened, the GEM (generic electronic module) remains awake for 1 minute if no action is triggered. If an action is triggered, the GEM (generic electronic module) remains awake for at least 16 minutes.
The GEM (generic electronic module) wakes up when it receives a signal from any of the following:
^ The K bus
^ Any door status switch (driver, front passenger, LH (left-hand) and RH (right-hand) rear doors)
^ Hood ajar switch
^ Central locking switch
^ Driver's door lock cylinder lock switch
^ Driver's door lock cylinder unlock switch
^ Interior lamp switch
^ Lower tailgate opening switch
^ Tilt alarm sensor
^ Ultrasonic sensor
^ Upper tailgate opening switch
^ Upper tailgate status switch.
GEM Harness Connectors
GEM Harness Connector C0660 Pin Details
GEM Harness Connector C0661 Pin Details
GEM Harness Connector C0662 Pin Details
