Rain/Light Sensor, Basic Function - GF54.21-P-2005A

Model all (CAR) 

Overview 

This document contains information on:

• General 
• Function 

Courtesy of MERCEDES-BENZ USA

General 

The rain and light sensor is located on the inside of the windshield in the area of the inside rearview mirror.

The following sensors are integrated into the rain and light sensor:

• Rain sensor
• Light sensor
• Humidity/temperature sensor
• Head-up Display light sensor (vehicles with Head-up Display)
• Sun sensor

Function 

The rain and light sensor detects the following conditions:

• Background light intensity

  The light sensor records the ambient light intensity.

  The Head-up Display light sensor (vehicles with Head-up Display) records the road brightness in the viewing direction.

• Degree of windshield wetting

  The rain sensor detects the degree of wetting of the windshield. An infrared transmitter unit beams infrared light at a defined angle to the interior of the windshield, which is almost completely reflected when the windshield is dry. If there are water droplets outside on the windshield, a considerable part of the infrared light is diverted.

  The intensity of the reflected infrared light is correspondingly lower.

  The lower the measured light intensity, the higher the degree of wetting of the windshield.

• Air humidity and temperature on inside of windshield

  The humidity and temperature sensor measures the relative air humidity and the temperature directly at the inside of the windshield. The data are used to calculate the dew point temperature and the surface temperature of the windshield. This enables any (imminent) windshield fogging to be detected.

• Intensity of solar radiation

  The sun sensor records the intensity of the solar radiation in the vehicle. Depending on this, the control of the climate control adapts the vehicle interior temperature and the blower setting.

  The rain and light sensor is networked with the front signal acquisition and actuation module.

  To reference the signals from the integrated sensors, the rain and light sensor evaluates, among others, the following information:

• Terminal status of terminal 15
• Outside temperature
• Vehicle speed
• Windshield wiper, status
• Request for sensitivity of light sensor
• Request for sensitivity of rain sensor

The rain and light sensor also sends the following signals:

• Ambient light intensity (dimness stages)
• "Switch on low beams" request
• Windshield wiper request
• Dew point temperature, surface temperature of windshield
• Intensity of solar radiation
• Diagnosis information