Rain/Light Sensor: Function

Pressing the button on the wash/wipe switch activates the rain sensor. When the rain sensor is active, the green LED on the wash/wipe switch lights up.

When the rain sensor is activated, visual acknowledgment 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 windscreen 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 windscreen, full reflection of the infrared light is no longer possible. Part of the light penetrates the windscreen so that only part of the light arrives at the receiver diodes. The evaluation electronics identify the level of windscreen wetting from the reduction in light quantity and transmits a signal via the K-CAN data bus. The wiper module then runs a wipe 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 wash/wipe switch.

Each time the knurled 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.

Prerequisites  for trouble-free operation of the rain sensor are:

• Wiper blades OK 
• Sensor area free of soiling (road salt, insects)
• No streaking on the windscreen
• Windscreen in the area of the rain sensor without faults (stone chipping)
• Optical element bonded free of bubbles with the windscreen glass