I am having a issue with the rear defrost button on the screen and the actual button itself. The screen will sometimes show the rear defrost button icon in a gray color and you cannot click on it. The button when pressed blinks and shuts back off. An sometimes the screen icon is available to press and when you press the button it starts to work as well. I have taken it to the dealership twice now. I bought the vehicle used. They see the issue but when they put it on the scanner it doesn't show anything. They even did a re-climate of the system and still. The issues comes back and turns off any suggestions???