Hey, a couple of weeks ago the rear parking sensors just gave a constant tone when reversing. They were fine the night before but not the next morning. Now I don't know if i have original/genuine sensors or aftermarket but when I had the car on the ramp they appear to be really well fitted and are bosch sensors which i'm told a lot of manufacturers use. The 2 side ones are higher and the 2 in the middle are lower down the bumper. the 2 lower ones have the paint peeling and one has some contaminant. Is there any way to test whether or which sensor is faulty or whether its the control box?