Rain/Light Sensor
Rain/Light Sensor
Rain/light sensor
The rain/light sensor comprises the following sensors and components:
- Rain sensor: consists of 4 individual sensors that pick up the precipitation quantity on the windscreen.
- Driving light sensor: consists of 2 photosensors that pick up the brightness of the ambient light and of the frontal light.
Brief component description
The rain/light sensor is bonded to the inside of the windscreen in the wiper range of the windscreen wiper.
This installation location ensures that the sensor surface remains free of dirt and ice. To prevent the sensor surface from fogging over, the sensor is heated.
The rain/light sensor is supplied with voltage by the junction box via terminal 30g. The rain/light sensor is connected via the LIN bus with the junction box electronics.
Rain sensor
The rain sensor is an optical sensor. It consists of an optical element. The optical element is firmly bonded to the windscreen. An electronic component is also integrated. Alongside the evaluation electronics, 4 optical transmitter and receiver diodes are integrated in the electronic component.
Driving light sensor
The driving light sensor is also an optical sensor. It consists of 2 photosensors and the corresponding evaluation electronics. One photosensor is aligned forwards and it picks up the light that strikes the front (frontal light). The second sensor is aligned upwards and it picks up the light striking from above (ambient brightness).
System functions
The following system functions are described for the rain/light sensor:
- Detection of precipitation
- Detection for driving lights
Prerequisites for trouble-free operation of the rain sensor are:
- Wiper blades OK
- No streaking on the windscreen
- Sensor area free of soiling (road salt, insects)
- Windscreen in the area of the rain sensor without faults (stone chipping)
- Optical element bonded free of bubbles with the windscreen glass
Detection of precipitation
If intermittent mode is switched on at the wash/wipe switch, the rain sensor is activated (lightly push the drop arm upwards). First of all, one wipe cycle is run as visual acknowledgement of the switching on. Then, the 4 transmit diodes emit infrared light that is routed via the optical element to the windscreen. If the windscreen is completely dry and clean, the infrared light is fully reflected to the 4 receiver diodes.
If there is water or dirt in the area of the optical element on the windscreen, the infrared light is refracted. This means that only part of the infrared light is reflected to the receiver diodes. The amount of reflected light is thus the measurement of the intensity of the precipitation in the area of the optical element. The evaluation electronics use the missing amount of light to detect the degree of wetness on the windscreen. They transmit a signal via the LIN bus. On the basis of this signal, it is assessed in the junction box electronics whether a wipe cycle is necessary.
With the vehicle stationary, the sensitivity is adapted automatically. The windscreen wiper is switched to intermittent operation. On switching off terminal R, the rain sensor is switched off for safety reasons. To reactivate the rain sensor, the intermittent mode must be set again at the wash/wipe switch.
Detection for driving lights
When the light switch is in the position for automatic driving lights control, the driving light sensor is activated. The change in lighting conditions in front of the vehicle and in the environment of the vehicle is picked up by the light-sensitive sensors. The lighting condition is processed by the evaluation electronics and transmitted via the LIN bus to the junction box electronics. Depending on the brightness, with the automatic driving lights control active, the driving light is switched on and off.
Notes for Service department
The following general information about the rain/light sensor is provided for service staff:
General notes
A dry and undamaged windscreen surface is necessary for installation of the rain/light sensor. The sensor must always be cemented to the windscreen without any trapped bubbles. For trouble-free operation of the rain/driving light sensor, there must be no streaks on the windscreen. Moreover, the wiper blades must be OK.
Diagnosis instructions
Initialization of the rain sensor
To ensure that the optical measuring procedure for the detection of precipitation functions properly, the rain sensor must be adapted to the windscreen.
A prerequisite for trouble-free initialization is that the windscreen glass is dry, clean and free of defects in the area of the rain sensor.
The initialization is performed using the "Initialize rain sensor" service function in the BMW diagnosis system. This service function deletes the adaptation values in the rain sensor.
Special feature: Initialization is only carried out after a terminal change. As the rain/light sensor is supplied via terminal 30g by the junction box, there are the following possibilities to carry out the initialization:
- Allow the vehicle to go to sleep
- Briefly remove the fuse for terminal 30g in the junction box
After a 10-second waiting period, the new adaptation values are determined automatically and stored by the sensor.
Are-initialization of the rain sensor is required:
- After replacing the windscreen
- After installation of a rain/light sensor
Notes on encoding/programming
Encoding
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.
The formation of bubbles/blisters on the bonding surface of the optical element impairs the lighting function We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.