Central Electronic Module (CEM) (2006-2013): Design: Siren
Information from the siren control module (SCM) to the central electronic module (CEM) contains configuration and status data. This information is transmitted using serial communication.
When the alarm is activated, the siren control module (SCM) transmits continuous status signals to the central electronic module (CEM).
The siren has a battery and a built in battery charger so that it is independent of the power supply in the car. The battery charger maintains battery voltage in the integrated battery. When the alarm is activated, the power to the siren and the serial communication between the siren control module (SCM) and the central electronic module (CEM) is monitored. If the power supply for the car to the siren is broken, or the communication between the central electronic module (CEM) and siren control module fails, the siren starts to sound. The battery and battery charger in the siren cannot be replaced separately. The entire siren must be replaced in the event of a fault.
The siren is below the plenum chamber on the passenger side. After replacement, a new siren control module (SCM) must be configured. This is done using VIDA (Volvo scan tool).
There are diagnostics for the siren.