Aqustick Parking Assist

The Aqustick Parking system on my '02 A6 is acting up. Somtimes it workes as it should but somtimes there is just a long warning tone when i put in
reverse. Anyone know how these sensors work? The sensor has 3 pins and it look like it is supplied 12V on two of the pins. The third pin must be output. But whoat does it output? Will the diagnosis system be able to tell wich sensor of the four is broken if one is?
Jone Tytlandsvik
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