I recently upgraded to a 2012 Chrysler Town & Country Touring-L. One feature on this minivan is what I'm calling "auto wipers": the front wipers automatically engage when the windshield becomes unclear due to water, and the wipers' speed adjusts in response to how heavy the water is.

How is this feature implemented, what are its failure modes, and how would I go about repairing them?


How does an Rain sensing wiper work?

  • Most modern cars have a device called a Optical Rain Sensor fitted onto the windscreen to detect rain and other obtrusive material. It simply works by firing an infra-red wave at an angle (45 degrees) from one side towards a receptor. When there is nothing on the wind shield the receptor picks up the infra red wave and nothing happens but when something like rain hits the windscreen, due to refraction the wave changes path and does not hit the sensor which detects the abnormality and activates the wipers.

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  • Issues might can occur in there places. Sensor, Processor, LED.

As far as I know , OEMs change the entire assembly and not the above components individually, Cheap ones might have separate fixtures.

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  • So to sense how much water there is it just uses an array of these? – clcto Jul 27 '15 at 21:53
  • @clcto Usually only one is enough, since for small drips you dont need to activate the wiper. they will be located near the rear view mirror on most cars. – Shobin P Jul 28 '15 at 7:46
  • I think the idea is based on total internal reflection as follows: At incidence angles around 45 degrees or shallower, the glass/air interface reflects essentially all of the light. The detector is positioned to receive this reflected light. Water has a similar refractive index to glass, so total internal reflection at the glass/water interface only occurs at much shallower angles, so more of the light passes into the water drop to ultimately follow some other path than into the detector. Less light on the detector means more water on the windshield. – Anthony X Jun 24 '17 at 23:18

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