Here is success and failure experience of Audi TT 2003 KM change, using different odometer correction tools.
Car: Audi TT 8n 2003 D73
I got connection but I only get error message from the device when I want to enter the mileage option.
It is very recommended tool to do that. So I bought one of it but with that tool nothing change.
It seems to work ok. I enter the mileage and continue. Then car-display restart and the Digiprog 3 says to remove fuse but nothing changed, still the same mileage. I tried also to disconnect the battery but it also not help, or did I removed the wrong fuses^^ I used 11 and 15 which are both for the speedometer. I also tried it separate, so only to remove one fuse.
Regarding your cluster, it probably contains a MC912DG128ACPV MCU that contains the mileage data so you need a tool that can read and write that to that chip. Quite a few of the more well known tools can’t read and write to it over OBD (Chinese clones are some of the well known ones for corrupting this chip and causing the 999999 error). You should avoid taking risks with writing to this chip as it could corrupt your immobiliser/key data and then cause your car not to start, the immobiliser cutting the engine off.
If you want change mileage with a cheap tool, go to a man of his words to trust in.
Note that: Different tools might have diff connections and colours of wires
Required cable – C12:
How-to’s & connection:
1.Remove the dashboard and open it carefully.
2.Remove the back side of the dash to get to the main board and identify it.
3.Solder cable C12 to the points on the back of the dash mainboard
4.Make sure that the connection you made is secure.
5.Use the EDITOR to save memory backup data.
6.Press the READ KM button and check if the value shown on the screen is correct.
7.Now you can use the CHANGE KM function.
TRY ON YOUR OWN RISK!