FREE REPAIR MANUALS & LABOR GUIDES 1982-2013 Vehicles
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Ambient Light Sensor: Description and Operation

Rain Sensor:




The rain sensor provides the primary input for the optional automatic wiper system. The rain sensor is located on the inside of the windshield, where it is concealed within the molded plastic trim cover that snaps over the base of the rear view mirror arm. The sensor fits within the center of a ring-like molded plastic bracket that is glued to the inside of the windshield glass and that also serves as the support for the rear view mirror.

The rain sensor is contained within a circular molded black plastic housing with a short pigtail wire and a connector insulator containing three terminal cavities that exits one side of the housing. This pigtail connects the rain sensor to the vehicle electrical system through a dedicated take out and connector of the overhead wire harness that extends from above the headliner. A molded plastic trough routes and conceals the pigtail wires on the inside of the windshield between the rear view mirror base and the headliner.

The windshield side of the rain sensor housing is open, but covered with a clear gelatin-like material that protects the internal electronic sensor circuitry and serves as the lens for the Infrared (IR) diodes and photocells within the sensor housing. This gel coating must never be touched or the rain sensor function may be impaired and the unit rendered unusable. The rain sensor cannot be adjusted or repaired and, if damaged or faulty, the entire sensor must be replaced. The sensor bracket and a rear view mirror adhesive kit are available for separate service replacement.

The rain sensor operates on battery current and a clean ground received from the rain sensor control module. The rain sensor contains Infrared (IR) diodes that direct IR light beams at the windshield at an angle. When the windshield glass is dry, most of this IR light is reflected back to the sensor, which uses photocell receivers to measure the intensity of the light. When moisture accumulates on the windshield glass, much of the IR light is refracted away from the photocell receivers. This causes changes in the signal output of the rain sensor. The rain sensor control module monitors the signal output from the sensor and then controls the wiper motor speed and wipe intervals accordingly.

It is important to note that the default condition for the wiper system is automatic wipers Off; therefore, if no message is received from the rain sensor by the rain sensor control module, the automatic wipers will be disabled. If automatic wipers are disabled, normal low and high speed continuous wiper operation are unaffected. Also, due to the low voltage nature of the rain sensor signal and the impact that minor fluctuations in this signal strength can have on wiper operation, grounded shielding circuits are provided at the roof and control module connectors to control electrical induction into the sensor signal circuit.

The hard wired rain sensor circuits may be diagnosed using conventional diagnostic tools and methods. However, conventional diagnostic methods may not prove conclusive in the diagnosis of the internal circuitry or the optics of the rain sensor. Refer to the appropriate wiring information.


RAIN SENSOR CONTROL MODULE

Rain Sensor Control Module:




The Rain Sensor Control Module (RSCM) is the primary component of the automatic wiper system. The RSCM is secured with two screws and nuts to a bracket located under the instrument panel above the throttle pedal within the passenger compartment. The rectangular molded plastic housing of the RSCM has an integral mounting tab on each side and an integral connector receptacle on one end, which contains the module terminal pins. These terminal pins connect the RSCM to the vehicle electrical system through a dedicated take out and connector of the instrument panel wiring. Concealed and protected within the RSCM housing is the electronic circuitry of the module.

The RSCM cannot be repaired and, if damaged or faulty, the entire module must be replaced.

The microprocessor-based Rain Sensor Control Module (RSCM) is only used in vehicles equipped with an optional automatic wiper system. The RSCM monitors inputs from the ignition switch, the wiper and washer switch circuitry of the multi-function switch on the steering column, the park switch within the wiper motor, and the rain sensor on the inside of the windshield glass. Based upon these inputs the RSCM sends the proper control outputs to the wiper motor and the washer pump motor to provide all of the requested wiper and washer system functions.

The RSCM operates on battery current received from a fuse in the fuse block on a fused ignition switch output (run-start) circuit so that the RSCM will operate whenever the ignition switch is in the On or Start positions. The RSCM receives ground at all times through its connection to the instrument panel wire harness. It is important to note that the default condition for the wiper system is automatic wipers Off; therefore, if no input is received from the rain sensor by the RSCM, the automatic wipers will be disabled and the RSCM will default the wiper and washer system to normal manual operation for continuous low or high speed wiper or washer mode.

The hard wired RSCM circuits may be diagnosed using conventional diagnostic tools and methods. However, conventional diagnostic methods may not prove conclusive in the diagnosis of the internal circuitry of the RSCM. Refer to the appropriate wiring information.