I have been browsing the web for a solution for this for weeks. Finally i came over this post, and it seems to be the same problem I have got. I have an Audi A6 Avant 2.5 TDI, 2003 with Navi plus. I have the exact same error message in the display, and the same symptoms (no RDS or navi info in the instrument cluster).
I scanned the car for error codes using VAG Com, and here are the fault codes i found:
Thursday,28,February,2008,16:28:19:06987
VAG-COM Version: Release 704.1
Data version: 20071016
Chassis Type: 4B - Audi A6 C5
Scan: 01 02 03 06 08 15 16 17 18 34 35 36 37 45 55 56 57 65 67 75
76 77
-------------------------------------------------------------------------------
Address 17: Instruments Labels: 4B0-920-***-17.LBL
Part No: 4B0 920 933 G
Component: KOMBI+WEGFAHRS. VDO D12
Coding: 00060
Shop #: WSC 00795
WAUZZZ4B43N1026 AUZ7Z0C23899
2 Faults Found:
01300 - Control Module for Navigation with CD-Rom (J401)
49-00 - No Communications
01304 - Radio
49-00 - No Communications
-------------------------------------------------------------------------------
Address 37: Navigation Labels: None
Part No: 4B0 035 192 K
Component: RNS 4.2 H06 BNO 0105
1 Fault Found:
01317 - Control Module in Instrument Cluster (J285)
49-00 - No Communications
-------------------------------------------------------------------------------
Address 56: Radio Labels: None
Part No: 4B0 035 192 K
Component: Radio BNO 0001
Coding: 00207
Shop #: WSC 67083
2 Faults Found:
00856 - Radio Antenna
36-10 - Open Circuit - Intermittent
01317 - Control Module in Instrument Cluster (J285)
49-00 - No Communications
-------------------------------------------------------------------------------
By reading the posts above it seems to me that this TMC box should be located behind the instrument cluster. I also checked out this link:
TMC BOX CAN GATEWAY Audi Navigation plus on eBay, also, Cavi, Spine e Accessori, Autoradio e Monitor, Auto ricambi e accessori (end time 29-Mar-08 00:40:51 GMT)
The box I found using this link looks identical to a box that is installed on the right hand side of the drivers foot well (left hand steering) in my car. My question would be where I can expect to find this TMC box (behind the instrument cluster or if this is the box I found on the side in the foot well)..??
Many thanks for any help....