Rain/Light Sensor With Additional Functions, Component Description - GF54.21-P-6005FH

Model 238 

Up To Model Year 2021 

Shown On Model 238.3 

Courtesy of MERCEDES-BENZ USA

Location 

The rain/light sensor with additional functions is located inside the windshield in the area of the inside rear-view mirror (A67).

Task 

The rain/light sensor with additional functions is responsible for the following tasks:

• Reading in of signals 
• Recording states 
• Sending signals 

Reading in of signals 

The rain/light sensor with additional functions reads in the following signals, amongst others, from the front SAM control unit (N10/6) via the rain/light sensor LIN (LIN B16):

• Circuit 15 status
• Outside temperature
• Vehicle speed
• Sensitivity of light sensor (B38/2b2)
• Sensitivity of rain sensor (B38/2b1)

Recording states 

The rain/light sensor with additional functions records the following states in the windshield area:

• Ambient light intensity through light sensor or through head-up display light sensor (B38/2b4) (with CODE 463 (Head-up display)) The light intensity of the vehicle's surroundings is detected by the light sensor.

  The "head-up display" light sensor records the road brightness in the viewing direction.

• Degree of windshield wetting through rain sensor

  The degree of windshield wetting is determined using a transmission, reception path. An infrared transmitter unit beams infrared light at a defined angle to the interior of the windshield, which is almost completely reflected onto an infrared receiver when the windshield is dry. If there are water droplets on the outer surface of the windshield, a considerable part of the infrared light is diverted. The intensity of the reflected infrared light is correspondingly lower and the reception signal of the infrared receiver is weakened. The lower the measured light intensity, the higher the degree of wetting of the windshield.

• Air humidity and temperature of inside of windshield through moisture/temperature sensor (B38/2b3)

  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 via sun sensor (B38/2b5)

  The interior temperature and the blower setting are adapted according to the intensity of the solar radiation on the vehicle.

Sending signals 

The rain/light sensor with additional functions sends the following signals, amongst others, via the rain/light sensor LIN to the front SAM control unit:

• "Low beams ON" request
• Ambient light intensity (dimness stages)
• Intensity of solar radiation

Wiring diagram for rain/light sensor with additional functions

PE54.21-P-2001-97DCA