There's a few things you can do before going to the dealer . First, make sure the wiper is cleaning all the water from the glass. A slight smear is all it takes to initiate another wipe. Next, look closely at the area of the windshield where the sensor is. Using a spray bottle, hit the area with a little mist. After the wiper passes over the sensor see if it leaves a slight haze. If it does, you can use some compound to thoroughly clean the area. Almost every time it rains, I get a few clients who come in with this problem. You'd be amazed at how often this happens. If you must go to the dealer, ask them if they can try re-adapting the sensor before replacing it. This works some of the time. Good luck