I tackled this today. So unnecessarily awkward...... and with a scorpion sting in the tail.
Rear seat base out, disconnect two little occupancy sensor wires and heated seat wires.
Then remove 4 x M8 blts holding the rear seat base rear hook points. Not sure why they need to be 30mm long.... 15 would have been ample.
Undo the lower centre seat belt anchor point
Then remove the two screws holding the wire loops on the bottom of the seat backs.... and after figuring out how to access them behind their little roller modesty blind the two M6 bolts in the centre. Then lift the seat back up to unhook from the upper mountings. Hard with one person, but possible.
Disconnect airbag wires and heated seat cables and wrest the seat out. It's heavy and awkward.
Now you can see the two plastic trim rivets holding the parcel shelf and winkle then out. You still can't get the parcel shelf out though as the (Bose) speakers are holding it.......
Into the boot and remove the 10 screws holding the two speaker covers to the underside of the parcel shelf.... and the two screws each side holding the speakers.... Back inside the car you can now left the speakers out and disconnect them.
Finally the parcel shelf can be slid forward and the buzzer accessed. It's held by two plastic trim rivets. What a daft place for it.....
Multimeter confirms it's open circuit. Fit new one after a bit of cussing as until I worked out I could put my arm through the speaker hole, it was looking like a two-person job to reassemble the rivets!
Reassembly is the reverse of removal..... (yes, I was a Haynes technical author briefly....) except that I reckon you need two people to get the rear seat back re-hooked....
Carefully plug everything back in and route the wires out of the way.
Parking sensors now work...... yay!.
Oh.... but wait..... now the airbag light is on. Have I offended the b@stard controller just by unplugging the wires without even turning the ignition on.....? Or have I failed to make one of the connections properly......?
Plug in VCDS lite...... can't to connect to the airbag controller. Will connect to everything else though, including the parking sensor controller which shows no error after the historical buzzer error was cleared.
Try connecting to the airbag controller twice more..... nope.
Try my superVAG 2. Nope that won't connect to it either...... though it will to other modules.
Try my Thinkcar dongle. That won't connect to anything, which is fairly normal, useless POC that it is.... .
Arrrgh..... so I've fixed one fairly trivial irritant and the car has rewarded me with a much bigger problem.......
Why do I bother with this 4 rings tat?!
Any clues/suggestions on the airbag welcome.....
Nick