Parking Sensor Problems

Hi all, I recently bought another B6. It's a well spec'd 1.9TDI Avant Quattro and needed a few issues sorted so I got a good deal on it. I've sorted most things out now but I'm having some issues with the parking sensors. The car has front and rear sensors which I believe are factory fitted, but when reverse is selected it emits a long beep to signify a fault and the green light on the parking sensor switch flashes.

I have a basic fault code scanner but it doesn't seem to be able to communicate with the parking assist module and so I haven't been able to identify the fault with this. All sensors emit 'clicks' when the car is in reverse however 1 of the front sensors is quieter than the rest and 1 rear sensor has a scratch through the middle but still clicks the same as the others.

Is it likely that the quieter sensor is failing and causing the problems, or do scratches affect the sensors? Also are all the front and rear sensors the same?

Thanks, Joe

Thanks for the reply and the info. I do most of the work on my cars and so I'll have a go myself, thanks for the offer though. Does anyone know if the part numbers for the front and rear sensors are the same?