Central Electronic Module (CEM) (2005-2006): Function: Headlamps

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2006 Volvo S80, 2005 Volvo S80, 2004 Volvo S80, 2003 Volvo S80, and 2002 Volvo S80. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Headlamps Communication Diagram

Courtesy of VOLVO CARS OF NORTH AMERICA.

Depending on the position of the knob, the light switch module (LSM) (3/111) transmits information via serial communication to the central electronic module (CEM) to turn on low beam. The central electronic module (CEM) (4/56) then transmits a control signal to activate the low beam relay. The bulbs are then supplied with power.

To change to high beam, the left-hand control stalk is pulled towards the steering wheel. The serial communication signal from the steering wheel module (SWM) (3/254) is transmitted to the central electronic module (CEM) which activates the high beam relay and supplies power to the high beam. For Bi-Xenon lamps, the position of the reflector is also changed so that the Xenon lamp is on at high beam.

The central electronic module (CEM) also transmits a CAN signal to the driver information module (DIM) (5/1) to light the indicator lamp for high beam.

There is a Limp Home function which ensures that low beam still works if there is a fault in the control area network (CAN). For Bi-Xenon lamps the beam is then set to the shortest range.