The radar cruise control system depends on an unobstructed path to the sensor located in the front nose above the grille. There are many things which can cause an obstruction and the warning light is there simply to do the job of telling the driver that the system is not functioning...the driver need do nothing, and in fact can do nothing to make it function again other than keeping the frontal area clean. The system will resume functioning by itself when the obstruction is cleared and that obstruction can be ice, mud, and at times even heavy rain...anything. Because of these issues, newer cars of all makes now have the system sensor in the grille unit behind a clear plastic sheet which is quite visible, usually surrounding a grille badge.