Just bought a 2010 TC XLT with the sensors. I'm near Chicago and the second and third days I had it the backup sensors were wailing. No ice, water or dirt on them... but I ran my finger over the sensors and it stopped wailing. No dirt evidenced... I am sitting in the service department now as they try to diagnose it. I have a feeling I will forever be wiping the sensors every time I get in the truck if they are to be of any use...