Had a look at a CLS55 today and was told the parking sensors weren't working on the rear. Turned out neither did, but I could do with some help guessing what the fault is. When driving, the "P Off" light seems to come on itself, thus disabling Parktronic. When I try backing or edging forward up to a wall and press it again to turn it back on, a loud alarm beep sounds for about 2 seconds and both sets of internal position lights show two lights per side, but do not change depending on how close you are to something. Seems to tend to disable itself again then if you drive. Ideas? Nothing came up on dash as an error.