Alarm, Electrical Control Modules, Brakes, Brake Control Module (BCM) - Design And Function: Alarm: Design: Siren
The siren is used as a sound source for the alarm function. The siren is mounted under the cowl. From structure week 200946 the siren is fitted in the left-hand wheel housing, above/behind the wheel. The siren is available with or without an internal vehicle tilt sensor. The type of siren mounted in the vehicle is market and customer dependent.
The siren sounds if the power supply is cut or if ground is cut or if communication with the central electronic module (CEM) fails while the alarm is activated. The siren contains an internal battery which is charged when the ignition is on. The battery cannot be replaced by itself. The alarm cause can be read from the diagnostic tool. This states what caused the alarm.
If the vehicle is equipped with a siren with a vehicle tilt sensor, the sensor is integrated into the siren. The vehicle tilt sensor reacts to changes in the angle of lean or motion of the vehicle and transmits a signal to the central electronic module (CEM). While the vehicle tilt sensor is mounted in the siren it is counted as a separate unit. If the vehicle tilt sensor indicates that the vehicle is being lifted the central electronic module (CEM) must send an activation signal to the siren. In this case the siren cannot trigger an alarm by itself.
The siren is powered via a fuse from the central electronic module (CEM) The siren is grounded in the engine compartment.