My check engine lights keeps turning on and then off every couple months. They said that it could be a bad sensor, the one that measure temperature for the transmission. They told me that I had to replace all of them, because they sold them in a set and that it would cost me about 400. Is that right? and do I really have to replace all of them. What would happen if I didn't. I don't know much about cars at all and need some help!!!