Light Rain Sensor Module (LRSM)

The LRSM senses moisture and ambient light levels on the outside of the windshield glass and sends electronic messages to the BCM over the LIN data bus. The BCM relays messages back and forth between the LRSM and other electronic modules in the vehicle.

For the rain sensor function, InfraRed (IR) diodes within the LRSM generate infrared light beams that are aimed by the optics of the sensor through the windshield glass, while an IR photo diode monitors the infrared light reflected back from the windshield glass. When sufficient moisture accumulates within the wipe pattern on the windshield glass, less of the infrared light is reflected back and the sensor detects a change in the monitored infrared light intensity. For the light sensor function, an IR photo diode within the sensor monitors the intensity of the ambient infrared light received through the windshield glass and the sensor optics.

The internal programming of the LRSM sends the appropriate electronic wipe command  messages to the BCM over the LIN data bus. The BCM then responds by activating or deactivating the wiper system. Similarly, the LRSM provides electronic ambient light level  messages to the BCM, and the BCM relays these messages to other electronic modules in the vehicle.

The BCM microcontroller sends electronic wiper switch status  and automatic wipe sensitivity level  messages over the LIN data bus to the LRSM based upon the driver-selected settings of the control knob on the control stalk of the right (wiper) multifunction switch. The higher the selected wipe sensitivity setting the more sensitive the LRSM is to the accumulated moisture on the windshield glass, and the more frequently the LRSM will send wipe commands  to the BCM to operate the wiper system.

The LRSM operates on battery current received through a fused ignition output (RUN/Accessory) circuit. The LRSM has a path to ground at all times through a take out of the body wire harness with an eyelet terminal that is secured to the body sheet metal. Therefore, the LRSM is operational only when the ignition status is ON or Accessory.

If the BCM receives an electronic status message from the LRSM indicating a sensor failure condition, a Rain Sensor Failure  message should be displayed by the Instrument Panel Cluster (IPC). It is important to note that the default operation of the automatic wiper system is continuous wipe ON. Therefore, if no command message is received by the BCM from the LRSM for more than about five seconds when the Automatic wipe mode is selected, the wipers will default to Low Speed or High Speed continuous wipe operation. The BCM must be properly configured for the automatic wipers in order for this system to function.

Newer models utilize a combination sensor that detects rain, humidity, solar, twilight and tunnel scenarios.