Rain/light sensor, component description - GF54.21-P-6000SX
MODEL 221.0 /1, 216.3 up to Model Year 8
Shown on model 221.0
Location
The rain/light sensor is located on the inside of the windshield below the inside rearview mirror.
Task
Measuring light intensity and quantity of water on windshield. Via the degree of wetting of the windshield the intermittent wipe of the wiper system (WSA) is controlled with two sensitivity stages. Various functions of the interior lights (IBL) and exterior lights (ABL) are controlled automatically via the light intensity.
Function principle for rain sensor
Infrared light is beamed from the infrared transmitter unit (1) and is directed to the windshield (3). The intensity of the light reflected at the windshield is measured by the infrared receiver unit (2).
If the windshield is dry in the area of the rain/light sensor (picture A), then the light is almost completely reflected and the infrared receiver unit measures a high light intensity.
If the windshield is wetted in the area of the rain/light sensor (picture B), then part of the light is scatted out of the windshield glass. As a result the intensity of the reflected light reduces and the infrared receiver unit measures a low light intensity.
The light intensity measured by the infrared receiver unit represents a measure for the degree of wetting of the windshield. The smaller the measured light intensity the greater the degree of wetting of the windshield.
The information is transmitted on the interior CAN via the overhead control panel control unit (N70).