Central Electronic Module (CEM) (2001-2004): Design: Headlamps

The headlamps at the front of the car are operated by the light switch module (LSM) which is positioned on the dashboard to the left of the steering wheel. The signals between the light switch module (LSM) and the central electronic module (CEM) are transmitted via serial communication. Low and high beam are operated by moving the left-hand control stalk towards the steering wheel.

The power supply for the lamps is via two directly connected relays on the central electronic module (CEM). One relay is for low beam and the other for high beam. The power supply for low beam is also via a shunt so that faults in the lamp can be detected.

For Bi-Xenon lamps the reflector in the lamp housing is moved by an actuator motor when changing between high and low beam. The actuator motor is integrated in the lamp housing.

There are three versions of the light switch function. These are programmed using the diagnostic tool:

• Low beam in all switch positions except the parking light position (flex zero)
• The light switch functioning on the basis of: off, parking light, low beam (flexsted)
• Low beam always on regardless of the position of the light switch (flexlgt).

To detect problems with the low beam, the central electronic module (CEM) reads the power consumption of the circuit. If this falls below a certain threshold value a fault will be indicated. The general warning lamp lights in the driver information module (DIM) and a text message is displayed.

For Bi-Xenon lamps there is a connection from the actuator motor to the central electronic module (CEM). In the event of incorrect values, the central electronic module (CEM) lowers the length of the beam using the headlamp range adjustment function.

There are diagnostics for the light switch and the relays.

There are also diagnostic for the high and low beam function (actuator motor) for Bi-Xenon lamps.