Theory Of Operation
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.
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 right (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 5 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.