Humidity Rain Light Sensor Module (HRLSM)

Rain Sensing Wipers Operating Conditions:

• Low Ambient Temperatures -  When the ignition is first placed in the ON position, the Rain Sensing system will not operate until the wiper switch is moved, vehicle speed is greater than 3 mph (5 km/h), or the outside temperature is greater than 32°F (0°C).
• Transmission in NEUTRAL position -  When the ignition is ON, and the automatic transmission is in the NEUTRAL position, the Rain Sensing system will not operate until the wiper switch is moved, vehicle speed is greater than 3 mph (5 km/h), or the gear selector is moved out of the NEUTRAL position
• Remote Start Mode Inhibit -  On vehicles equipped with Remote Start system, Rain Sensing wipers are not operational when the vehicle is in the remote start mode

The HRLSM combines the functions of the humidity, light and rain sensor modules into a single unit.

The HRLSM senses moisture and ambient light levels on the outside of the windshield glass as well as the humidity level inside the vehicle and sends electronic messages to the BCM over the LIN data bus. The BCM relays messages from the HRLSM and other electronic modules in the vehicle.

For the rain sensor function, InfraRed (IR) diodes within the HRLSM 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 HRLSM 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 HRLSM 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 HRLSM based upon the driver-selected settings of the control knob on the control stalk of the left (wiper) multifunction switch. The higher the selected wipe sensitivity setting the more sensitive the HRLSM is to the accumulated moisture on the windshield glass, and the more frequently the HRLSM will send wipe commands  to the BCM to operate the wiper system.

The HRLSM operates on battery current received through a fused ignition output (RUN/ACC) circuit. The HRLSM 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 HRLSM is operational only when the ignition status is ON or Accessory.

If the BCM receives an electronic status message from the HRLSM 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 HRLSM 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.