The rain/driving light sensor senses water or dirt on the windscreen and activates the windscreen wipers accordingly.
The RLS consists of an optical element bonded on the windscreen, to which an electronic evaluator is connected.
The system is active as of ignition lock position 1. The wiper/washer switch must be set to the first stage (intermittent wipe setting).
The wiper motor is activated by the general module. The electronic evaluator sends the activation command to the wiper motor via the K-bus to the general module.
The optical element is adhered to the windshield behind the rear-view mirror. It consists of a glass body (prism) which routes the beams emitted by infrared diodes at a defined angle to the windshield. The light beams reflected by the windshield are routed by the optical element to the infrared receivers.
The optical element is heated by a heating element to ensure condensation cannot form on it.
The optical element is bonded together with the windshield in a special process such as to guarantee the physical properties of the system. This bonding process cannot be carried out in the workshop. This means that when the windscreen is replaced a special windscreen with the optical element already bonded to it must be used.
The electronic evaluator is connected to the optical element by means of a catch mechanism.
It contains the electronic components as well as the infrared diodes and infrared receivers.
The activation command for the wiper motor is given via the K-bus interface.
Water on the windshield is detected on the basis of the reflection of infrared beams.
When the windscreen is dry, all of the beams sent out by the infrared diodes ”S” that hit the windscreen with a defined angle are fully reflected by the windscreen and thus reach the infrared receiver ”E” in full.
A proportion of these beams is deflected by a drop of water on the windshield (in the area of the infrared diodes). These beams no longer reach the infrared receiver ”E”.
Depending on the amount of light in the infrared beams that reach the receiver, the degree of wetness (or soiling) is determined and, if applicable, an activation command is sent across the K bus to the general module BC1 to the wiper motor.
To switch on the rain sensor, the wiper/washer switch must be moved up to the first stage (intermittent wipe) and the ignition lock must be switched to position 1 or 2.
The RLS then controls the wipe intervals. If the windshield is constantly wet (steady rain) the system activates continuous wiping in stage 1.
The wiper stage 2 can still only be set by way of the wiper switch (third stage).
If terminal R is switched off and on when the wiper switch is set to intermittent wipe, the RLS function remains off. It is not activated before intermittent wipe mode is switched off and on.
The following conditions are necessary to ensure trouble-free operation of the rain sensor:
To ensure trouble-free operation, the windscreen should be cleaned regularly with a suitable wax-removing cleaning agent. The wiper blades should be replaced regularly.
The reflection characteristics of the windshield depend on a large number of factors. In addition, these characteristics also change as the windscreen ages.
During the initial wipe cycles, a new electronic evaluator determines the degree of reflection of the windshield and stores this data in its non-volatile memory. From this point on, this data is constantly adapted to the windshield which is subject to a certain degree of aging over the course of time.
The stored adaptation values can be deleted with the diagnostic program (service functions). Renewed adaptation (initialization) to the windshield can then be carried out.
The initialization procedure is described in the program sequence.
Initialization is necessary:
The driving light sensor consists of two photodiodes and an electronic evaluation unit. The photodiodes are arranged in such a way that both light striking the sensor from the front and light striking the sensor from above (ambient light) are sensed.
If there is a change in the light conditions, a signal is sent across the K bus. When the Automatic Light Control is switched on, the general module switches the low-beam headlight on or off.
The light sensing is active as of terminal R, independent of whether the automatic driving light system is switched on or off.
The driving light sensor is adapted to the windscreen via coding. This is why a used sensor must be recoded on installation!