Detection of precipitation

WARNING: This page is about a different car, the 2013 BMW X5, 2012 BMW X5, and 2011 BMW X5. However, it is still accessible from the selected car via links, so may be relevant.

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

First of all, one wipe cycle is run as visual acknowledgment of the switching on. Then, the 3 transmit diodes emit infrared light that is routed via the optical element to the windscreen. If the windscreen is completely dry and clean, the infrared light is fully reflected to the 3 receiver diodes.

If there is water or dirt in the area of the optical element on the windscreen, the infrared light is refracted. This means that only part of the infrared light is reflected to the receiver diodes. The reflected light quantity is thus the measurement of the intensity of the precipitation in the area of the optical element. On the basis of the missing quantity of light, the evaluation electronics detect the degree of wetness on the windscreen glass and transmit a signal via the bus. On the basis of this signal, the junction box electronics (JBE) evaluates whether a wipe cycle is necessary.

The sensitivity of the rain sensor can be varied in 4 sensitivity stages by means of a knurled wheel on the wash/wipe switch. Each operation of the knurled wheel towards "Increase sensitivity" (i.e. turning the knurled wheel upwards) runs a wipe cycle. With the vehicle stationary and failure of the rain/light solar sensor, the windscreen wiper is switched into a fixed intermittent operation mode. On switching off terminal R, the rain sensor is switched off for safety reasons.

As of 09/2011, the protection function "Ice detection" will be introduced. At outside temperatures of below 0 °C (observe outside temperature display in the instrument panel) and with the rain sensor activated, automatic wiper operation is not possible. The following functions are suppressed:

Single wipe if automatic wiper operation is activated
The other wiper cycles if the windscreen is wet

As a result of the suppressed functions, possible damage to the windscreen wiper, for example due to frozen wiper blades, is avoided.

When a speed of 7 km/h is exceeded after the engine start for the first time, the protection function "Ice detection" switches off automatically. As of this time, automatic wiper operation is possible once again without restriction until the next time the engine is switched off and the vehicle enters the sleep mode.

Manual wiper operation is not affected by the protection function "Ice detection". That means: wiper stage 1 and wiper stage 2 can always be set manually.