Central Electronic Module (CEM): Function: Headlamps: Notes

Depending on the position of the knob in the light switch module (LSM) (3/111), the module transmits a request to the central electronic module (CEM) to switch on low beam. Central electronic module (CEM) (4/56) supplies power to the low beam directly via an output.

The level of the supply voltage to the low beam is controlled using pulse width modulation of the central electronic module (CEM). This means that the average value of the voltage level to the low beam does not exceed 13.2 V, despite the fact that the supply voltage may be higher.

To change to high beam, the left-hand control stalk is pulled towards the steering wheel. A signal is sent via LIN communication from the steering wheel module (SWM) (3/130) to the central electronic module (CEM), which activates the internal 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.

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.