I get the restricted visibility warning every now and then, most of the time when it's raining heavily so it's understandable. However, it often happens when it's particularly sunny on damp mornings as the sensors are overloaded with light from from the sun and the road. I have not put this down to a fault with the sensor in my car, more to do with a poor design. I often carry a cloth in the car and wipe over the grille sensor if it's wet or dirty.