Rain Sensor
The rain sensor module optically senses water on the windshield. An infra red beam of specific intensity lights a section of the windshield. The intensity of the reflected beam is measured and compared to the intensity of the transmitted beam. If there is water on the surface of the windshield, the beam distorts, reducing the intensity of the beam. If the beam is not reflected completely it is interpreted as rain on the windshield and the windshield wipers are started.
The signals from the upper electronic module are carried via serial communication. The rain sensor transmits the signals to the upper electronic module. These signals request a particular windshield wiper speed (depending on the amount of rain falling on the windshield), indicate that a sudden large splash has hit the windshield and register the light conditions outdoors.
The rain sensor is located in front of the rear view mirror on the inner side of the windshield. A special windshield is used on cars with rain sensors.
There are diagnostics for the rain sensor.