Body control unit (Operation): Description and operation (page 2 of 2)

When the alarm system is set the BCU checks the status of all the inputs from the door and bonnet switches to ensure the integrity of the vehicle before setting the alarm system into operational mode. In some markets, when the alarm is set the BCU sends a signal to the IDM which will cause the direction indicators to flash three times for a duration of 3 seconds.

If the sensors are triggered the BCU will activate an alarm sounder to provide an audible warning of a theft attempt. The activation period of the alarm sounder is 25 to 30 seconds. The duty cycle of the alarm sounder is 50:50 ± 10%.

In some markets, when the alarm is triggered the BCU also activates the direction indicators, in phase with the audible warning, to provide an optical warning of a theft attempt. The activation period of the optical alarm is 25 to 30 seconds. The duty cycle of the optical warning is 50:50 ± 10%.

The alarm system relies upon the vehicle battery for power. However, the BCU remembers the status of the security system if it loses battery supply. If the security system was in a set condition when battery supply was lost the BCU will trigger the alarm and initiate a visual warning by flashing the hazard lamps when the battery voltage is restored. On vehicles with a BBUS fitted, the BBUS will sound if the battery is disconnected while the alarm system is set.

Door switches The BCU uses the door latch switches to indicate if a door is open or closed. The BCU provides power to all door latch switches; the switches are in the 'normally open' condition when the doors are shut. When a door is opened, the door switch contacts are closed and the circuit is earthed, signalling a change in state to the BCU. All doors except the driver's doors are connected in parallel, so the BCU will recognise a passenger door has been opened but will not be able to distinguish which one. The driver's door has a dedicated signal line which enables the BCU to detect if the driver's door has been opened or closed.

Door lock actuators The CDL system has the facility to enable superlocking. All door lock actuators are controlled by the BCU via the IDM. The driver's door is controlled separately from all other doors, enabling functions like single point entry and key access.

Driver's door key lock and unlock switches The BCU uses the driver's door key lock and unlock switches to activate and deactivate the security system. The driver's door lock is also used for entering the EKA code.

Two separate switches are incorporated into the key lock assembly of the driver's door. The switches are normally open and the BCU provides a separate power supply to each. The BCU is signalled when a circuit is earthed enabling it to determine the direction in which the lock has been turned.

Bonnet switch The bonnet switch is powered from the BCU and is used as a logical input for operation of the security system. The switch is normally open with the bonnet closed, when the bonnet is opened the switch contacts close to complete a circuit to earth and signal the change in state to the BCU.

Key-in sensor When the ignition key is inserted into the lock barrel the key-in sensor contacts close and supply a signal to the BCU. The BCU monitors the ignition switch for a change in state and triggers the alarm if it receives an ignition signal before it receives an alarm disarm signal.

Another feed to the ignition switch is provided by the BCU to provide switch illumination.

A key-in warning can be enabled or disabled. When the key-in warning is enabled, an audible warning is generated if the ignition key is in and the driver's door is opened.