I picked up my car a few weeks ago, and foruntately it was mostly clear of faults in VCDS / OBDeleven. However there was one persistent fault in the MMI (Module 4F) relating to the GSM antenna system:

3086 - Antenna for Telephone Mount 
          B1564 01 [009] - Electrical Failure
          Confirmed - Tested Since Memory Clear
             Freeze Frame:
                    Fault Status: 00000001
                    Fault Priority: 4
                    Fault Frequency: 1
                    Reset counter: 76
                    Mileage: 132416 km
                    Date: 2023.12.22
                    Time: 12:14:34

                    Voltage terminal 30: 14.9 V
                    Status of telephone-Antenna diagnostic: OK
                    Status of telephone-Telephone baseplate diagnostic: not connected
                    Status of telephone-Handset in handset holder (cradle): selected
                    Status of telephone-Handset holder (cradle): connected

The car is a 2015 Audi A6 C7 with Tech Pack, which apparently included a function called Audi Phone Box. This gives you a small rubber mat under the armrest, and it’s linked to a signal booster which re-broadcasts the GSM/4G signal to an antenna in the boot of the car. Here’s a picture of the rubber mat:

Phone Box Mat

I initially thought that this was for Wireless Charging, but my car does’t have that - some do, and there is a slightly different logo on them.

Unfortunately, Audi somehow didn’t realise that GSM repeaters / boosters are completely illegal in the UK so any cars with this option installed needed to have it removed, either prior to import, or during a recall campaign. The booster module electronics was removed, but of course the MMI still expected to see it, hence the error.

Using VCDS or any other tool to change your coding, or Adaptation values is DANGEROUS. If you make changes without full understanding, you can break your car. Don’t do it!

To supress this error permanently, the MMI module need to be coded to remove the missing module. It’s in Byte 15 of module 4F:

4F coding

Unselecting Bit 1 (Telephone Antenna Baseplate installed) and saving the new coding cleared the fault, and it has not returned so far.