The rain-driving light sensor has integrated sensors that sense the wetness on the windscreen glass and the ambient light.
The rain sensor is an optical system. It consists of an optical element bonded on the windscreen and an electronic element. The electronic evaluation unit and 4 optical transmitter and receiver diodes are integrated in the electronic element.
Operating button on the wiper switch activates the rain sensor. When the rain sensor is active, the green LED on the wiper switch lights up.
When the rain sensor is activated, visual feedback is given to the driver in that one wiping cycle is executed first. Then, the transmitter diodes emit an infrared light which is guided across the optical element to the windscreen. If the windscreen is completely dry and clean, the infrared light is fully reflected to the receiver diodes.
If there is water or dirt in the area of the optical element on the windscreen, full reflection of the infrared light is no longer possible. Part of the light penetrates the windscreen so that only part of the light arrives at the receiver diodes. The electronic evaluation unit detects on the basis of the missing quantity of light the degree of wetness on the windscreen glass and sends a signal across the K-CAN data bus. In response, the wiper module executes one wiping cycle. In the case of heavy rain, intermittent operation shifts into the continuous wiping mode.
A heating element integrated in the rain sensor prevents misting of the optical element or the diodes.
The sensitivity of the rain sensor can be varied in 4 sensitivity stages by means of the knurled wheel on the wiper/washer switch. Each time the adjuster wheel is moved in the ”Increase sensitivity” direction (upwards), a wipe cycle is carried out.
When the vehicle is at a standstill, there is an automatic reduction of the sensitivity so that the wiper usually runs in intermittent mode.
If the rain sensor fails, the wiper runs at a fixed time interval.
For safety reasons, the rain sensor is switched off when terminal R is switched off.
Requirements for faultless operation of the rain sensor are:
Due to the optical process, the rain sensor has to be adapted to the windscreen. This adaptation takes place at initialisation.
Requirement for faultless initialisation is that the windscreen glass is dry, clean and free of defects in the area of the rain sensor.
The initialisation is performed using the service function ”Initialise rain sensor” in the BMW diagnosis system. In the service function, the adaptation values in the rain sensor are deleted. This is followed by adjustment of the sensor system to the windscreen based on the following sequence:
In the 10 seconds waiting period, the new adaptation values are determined and stored.
Initialisation of the rain sensor 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 lighting conditions, a signal is issued across the data bus K-CAN. When the automatic driving light system is active, the light module switches the driving light 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.
After replacement, the driving light sensor must be coded via the vehicle order and is thus adapted to the windscreen.