Sometimes they function perfectically and they will not work at all. My mechanic had my car today, could not determine the exact cause. They were working perfectically. He attempted to induce the problem through vibration to included tapping on the wiper motor, and the wipers continued to work. He said that if only he could see them when they are not working,then could he accuately determine the cause. He that the problem is in either the wiper motor or the wiper on and off switch. I have also tried to get clues to the cause. This afternoon, I started the car and fliped the switch. They did nothing. I popped the hood, and tapped on the wiper motor----NO GO. As soon as I dropped the hood----WORKING.