Rain Sensor: Description and Operation
SENSOR-RAINDESCRIPTION
The Rain Sensor is the primary component of the automatic wiper system.
The rain sensor is located on the inside of the windshield, just below the rear view mirror mounting button (1).
Sliding cam locks (6) on each side of the top sides of the sensor (either side of the connector) secures the sensor to the mounting bracket (9) that is bonded (1) to the windshield glass. A small screwdriver can be used to push in the tabs until the slider protrudes from the opposing side of the sensor case (5). Concealed within the sensor housing (5) is the electronic circuitry (7) of the module, which includes four Infrared diodes, four photocells, and a microprocessor.
The rain sensor software is Flash compatible, which means it can be reprogrammed using Flash reprogramming procedures. However, if any of the hardware of the sensor is damaged or faulty, the entire rain sensor must be replaced. The rain sensor bracket (9) is serviced as a unit with the windshield glass. If the bracket is faulty, damaged, or separated from the windshield glass, the windshield must be replaced.
OPERATION
The microprocessor-based Rain Sensor senses moisture in the wipe pattern (1) on the outside of the windshield glass and sends wipe commands to the Front Control Module (FCM). Four Infrared diodes within the sensor generate infrared light beams that are aimed by four of the convex optical lenses near the base of the sensor through the windshield glass. Four additional convex optical lenses near the top of the sensor are focused on the infrared light beams on the outside of the windshield glass and allow the four photocells within the sensor to sense changes in the intensity of these infrared light beams. When sufficient moisture accumulates within the wipe pattern (1) of the windshield glass, the sensor detects a change in the monitored infrared light beam intensity.
The internal programming of the sensor then sends the appropriate electronic wipe command messages to the FCM over the Controller Area Network (CAN) data bus. The FCM responds by activating or deactivating the front wiper system. The CCN sends electronic sensitivity level messages to the rain sensor over the CAN data bus based upon the driver-selected sensitivity setting of the control knob on the control stalk of the multi-function switch. The higher the selected sensitivity setting the more sensitive the rain sensor is to the accumulated moisture on the windshield glass, and the more frequently the sensor will send wipe commands to the FCM to operate the front wiper system.
The rain sensor operates on battery current received through a fuse in the Power Distribution Center (PDC) on a fused B+ circuit. The rain sensor receives ground at all times through the body wire harness. It is important to note that the default condition of the automatic wiper system is low. Therefore, if no message is received by the FCM from the rain sensor for more than about five seconds when in the Auto sensitivity wipe mode, the wipers will default to a constant low wipe state.
The rain sensor ground and battery current inputs may be diagnosed using conventional diagnostic tools and methods. The most reliable, efficient, and accurate means to diagnose the rain sensor requires the use of a scan tool and the appropriate diagnostic information.