Ambient Light Sensor: Description and Operation

Rain / Driving Light Sensor
The rain-driving light sensor has integrated sensors that sense the wetness on the windshield glass and the ambient light.

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

Function
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 windshield 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 windshield, full reflection of the infrared light is no longer possible. Part of the light penetrates the windshield 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 windshield 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:
- No smear on the windscreen
- Sensor area free of soiling (salt, insects)
- Wiper blades OK
- Windscreen in the area of the rain sensor without faults (stone impact)
- Optical element bonded free of bubbles with the windshield glass

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

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

Requirement for faultless 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 service function "Initialize 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 windshield 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 seconds waiting period, the new adaptation values are determined and stored.

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

Driving Light Sensor
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.

Requirements for fault-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 across the data bus K-CAN. When the Automatic Light Control is active, the light 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 control system is switched on or off.

After replacement, the driving light sensor must be encoded via the vehicle order and is thus adapted to the windscreen.
Coding the rain / driving light sensor
Coding of the rain / driving light sensor is required:
- After replacing the windshield
- After replacement of a rain / driving light sensor

At each new start, the junction box electronics (JBE) check whether the coding data stored in the rain / driving light sensor match the coding data stored in the junction box electronics.
In the event of deviations, the junction box electronics run automatic coding of the rain / driving light sensor in accordance with the target coding data.

The automatic driving lights control provides a coding 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 triggering, 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 salt residues, insects or water smears. 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 smearing as the values are no longer able to change.

The formation of bubbles on the bonding surface of the optical element impairs the rain function

Light sensor:
Due to the high surrounding 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 on the bonding surface of the optical element impairs the light function

No liability can be accepted for printing or other faults. Subject to changes of a technical nature