Rain/Light Sensor

Rain/Light Sensor

The rain/light sensor has integrated sensors that sense the wetness on the windscreen glass and the ambient brightness.

Rain sensor
The rain sensor is an optical system. It consists of an optical element bonded on the windscreen and an electronic component. Alongside the evaluation electronics, 4 optical transmitter and receiver diodes are integrated in the electronic component.

Function
Pressing the button on the wash/wipe switch activates the rain sensor. When the rain sensor is active, the green LED on the wash/wipe switch lights up.
When the rain sensor is activated, visual acknowledgement 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 evaluation electronics identify the level of windscreen wetting from the reduction in light quantity and transmits a signal via the K-CAN data bus. The wiper module then runs a wipe 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 wash/wipe switch. Each time the knurled 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.

Prerequisites for trouble-free operation of the rain sensor are:
- Wiper blades OK
- Sensor area free of soiling (road salt, insects)
- No streaking on the windscreen
- Windscreen in the area of the rain sensor without faults (stone chipping)
- Optical element bonded free of bubbles with the windscreen glass

Initialization
Due to the optical process, the rain sensor has to be adapted to the windscreen. This adaptation takes place at initialization.

NOTE: Only the rain segment can be initialized. In the event of complaints regarding the automatic driving lights control, initializing the rain/light sensor is ineffective.

A prerequisite for trouble-free initialization is that the windscreen glass is dry, clean and free of defects in area of the rain sensor.
The initialization is performed using the "Initialize rain sensor" service function 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:
- Switching off the rain sensor
- Switch off terminal 15 and terminal R
- Switch on terminal R and terminal 15 and wait 10 seconds

In the 10-second waiting period, the new adaptation values are determined and stored.

Initialization of the rain sensor is necessary:
- After replacing the windscreen
- After replacement of the rain/light sensor

Driving light sensor
The driving light sensor consists of two photo-sensors and evaluation electronics. The photosensors 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.
The prerequisites for trouble-free operation of the driving light sensor are those of the rain sensor.
If there is a change in the lighting conditions, a signal is issued via the data bus K-CAN. When the automatic driving lights control 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 lights control system is switched on or off.
After replacement, the driving light sensor must be encoded via the vehicle order to adapt it to the windscreen.

Encoding the rain/light sensor
Encoding of the rain/light sensor is required:
- After replacement of a rain/light sensor

The automatic driving lights control provides an encoding possibility to change the sensitivity settings (Japanese version: changed sensitivity settings).

Restrictions due to factors inherent in the system
Rain sensor:
Soiling of the sensor surface can lead to unwanted activation, up to and including continuous wiping. If the soiling continues over a longer period, the system reacts with a reduction in sensitivity.
Soiling can be caused by road salt residue, insects or water streaks. The windscreen should therefore be cleaned from time to time using the wipe-wash function.
As the window wiper cleans the sensor surface, the wiper must not be worn. A worn wiper would diminish the measured values of the sensor by streaking as the values are no longer able to change.
Formation of bubbles/blisters on the bonding surface of the optical element also leads to impairment.

Light sensor:
Due to the high ambient brightness, fog cannot be detected by the light sensor.
The light sensor is sensitive to light in the infrared range. The infrared proportion is high if there is dense cloud cover. With lighter cloud cover or blue sky - above all in winter - the sensor receives considerably fewer infrared light proportions. This means the light sensor switches the light on earlier or leaves it on for longer.
In well illuminated tunnel entrances, startup can be delayed. The high level of illumination means that the measured values are above the switch-on threshold.
Formation of bubbles/blisters on the bonding surface of the optical element also leads to impairment.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.