Our 2010 RX450h doesn't always turn on the wipers when the windshield gets wet. The dealer told us that it is functioning normally. We have to turn off and turn on the wiper to auto for it to function the way we think it should.

 

The rain sensor is behind the rear view mirror. You can spray water here on a nonrainy day and see if the wipers activate. I found the sensitivity adjustment doesn't really make a difference.

 

to be honest the rain sensors on lexus vehicles aren't some of the best you can find out there. they work, but i won't say they are good. if you search other forums, you will see quite a lot of complaints in the GS and IS forums as well. a lot of owners with other brands of cars (including me with bmw), i find it sometimes frustrating to use the auto wipers in my lexus. a lot of times i give up and just do it manually

 

the ones on my 2RX are fine. In fact, I rarely (if ever) have to manually touch the stock

 

I agree with there being a wee bit of a problem. In my experience, the car seems to forget. I'll be driving in the rain and all is well in auto mode. I don't touch the wiper control and park and shut off the car. Come back, start the car and start driving but the wipers will not start automatically and I have to flip them to on and then back to auto for them to work.

Perhaps that is as intended, I haven't checked the manual.

 

This seems quite common on many of Lexus... Mine has this issue, too.

 

I think the sensor detects water movement on the windshield. If the droplets are just sitting still when you start the vehicle, the sensor won't see them. Once you are moving fast enough for the wind to move the droplets, the wipers will activate.

 

It doesnt sense movement, it senses light that is being blocked off by the rain drop

 

definitely not the case. so many times already when i start the car, the stalk is at the auto and the fog outside triggers the wipers immediately. **** me off