Hi all

I paid for a VCDS readout from a chap local to me. I wanted a general overview of the car as I've only had it a few weeks. One of the known issues was with the parking sensors and I wanted to see if VCDS would point me in the right direction. Here is the relevant section from the output:

Address 76: Park Assist        Labels: 8Z0-919-283.lbl   Part No: 8Z0 919 283 
   Component: Parkingsyst. A6 RDW D08  
   Coding: 01116
   Shop #: WSC 02334  
   VCID: 020199400EC6EA51FF-5054

1 Fault Found:
01549 - Supply Voltage for Parking-Aid Sensor 
            29-00 - Short to Ground
The symptom I have:

I put the car into reverse and 80% of the time I will get a loud continuous tone for about 5 seconds and then silence. Not another peep out of it even when I'm just millimetres away from an obstacle. 20% of the time when I put the car into reverse I get absolutely no sound at all.

What I've tried:

Unplugged the two connectors going to the parking module above the n/s/r wheel arch. Sprayed contact cleaner and reseated. No difference.
Removed all four parking sensors (mine is the Final Edition model with the sensors relatively accessible at the bottom of the bumper extension bit). Contact cleaned all plugs and sockets and reassembled. No difference.
Plugged each sensor back in one by one and put the car into reverse. Exactly the same symptom - will park assist work with only a limited number of sensors connected? I'm guessing not, so perhaps this last step was pointless.
Putting the car into reverse and quickly running to the back to try and listen to each sensors. I've done this with all four and I can't hear any of the clicking I've read about

Now, the 'Short to Ground' is a bit ambiguous (well, only because of my understanding of VCDS) - does the 29-00 identify a particular sensor? Could it be the module itself? I have seen modules on ebay for about 15 and I've ordered one new sensor for 9 just to swap it out with each of the four existing ones just in case it's one faulty sensor causing the problem. Of course, I'd like to troubleshoot in a more efficient way than simply throwing money at the problem, so I'd appreciate any suggestions.