Rain/Light Sensor (RLS)

The Rain/Light Sensor is standard equipment, it is installed below the base of the rear view mirror as in other models.

The rain/driving light sensor is an improved version of the first-generation AIC rain sensor.

An additional driving light sensor is integrated into the rain/driving light sensor.

This function is described separately in the vehicle lighting section.

Fig 1: Rain/Light Sensor (RLS) Components

Courtesy of BMW OF NORTH AMERICA, INC.

Modifications from the first-generation rain sensor:

There are now 4 optical measurement sections instead of 2 which provides improved identification of dirt, salt etc.
Integration of the light sensor function.
K-Bus interface
Flash Programmable EEPROM.

The measuring principle of the RLS is identical to that of the previous rain sensor (AIC, automatic interval control).

The rain detection function is based on the principle of total reflection against the glass-to-air boundary surface:

When the windshield is clean and dry, the infrared light transmitted by the rain/driving light sensor is fully reflected.
When the windshield is wet or dirty in the area of the reflective surfaces, the conditions for total reflection no longer exist. As a result, less light is reflected.

This change in the signal is evaluated by a microprocessor in the Rain/Light sensor (together with other signals, e.g. speed).

If necessary, a message is sent to the wiper module via the K-Bus.

The wiper module then:

Fig 2: Rain Detection Function Diagram

Courtesy of BMW OF NORTH AMERICA, INC.