Steering Wheel Controls Not Working After Aftermarket Radio Install (Audi A8 D2 2001)

[Laisvydas]

Hi everyone,

I’m reaching out to see if anyone has experience or can offer advice on a problem I’m facing with my Audi A8 D2 (2001) after installing a Kenwood DMX8021DABS. My car has the original RNS-D navigation system, along with the TMC module, and I’m using the factory steering wheel with audio buttons.

After installing the DMX8021DABS, everything works fine except the steering wheel audio controls. The volume and track buttons on the wheel no longer control the radio, and the steering wheel menu in the Kenwood head unit doesn’t activate. I’ve already tried the CTSAU001.2 and CTKENWOODLEAD2 adapters, but they don’t seem to make the buttons work.

The CTSAU001.2 adapter I’ve tried shows compatibility with the Audi A8 D2 (1994-2002), and I’ve searched online for other adapters for the Audi A8 D2. While many of them claim to fit, I’ve noticed that none of the adapters explicitly list compatibility with the RNS-D system. Based on this, I’m fairly certain that any adapter I buy will not work with my RNS-D system.

After some research, I found that Audi A8 D2 models prior to 2000 used analog signals for the steering wheel buttons, but I’ve read that my 2001 model might use a mix of analog and CAN bus signals due to the RNS-D system. I noticed on the schematic behind my old audio player that there were CAN-H and CAN-L connections in the connector, which may be related to the signal communication for the steering wheel controls.

Has anyone here successfully made the steering wheel controls work with an aftermarket radio in an A8 D2 (2001), especially with the mixed analog and CAN bus system? If so, could you recommend the correct interface or wiring setup to get it working? Any help would be greatly appreciated!

Thanks in advance!

[Ronin]

This is a very deep subject, but yes I've managed it.

First of all your factory fitted mfsw speaks to the mfsw relay in the footwell over single wire lin bus protocol.
Then, mfsw relay speaks to the car's infotainment canbus OR with single wire serial connection on mostly pre-facelift cars, NOT 'voltages'.

If you have TMC module fitted behind the cluster, you will need to intercept the can high and can low wires going into it, and join them with the can high and can low wires coming out of it into the head unit plug.
Then your connects2 adapters can translate those can messages into whatever the DMX needs.

This is because those incoming CAN messages get translated into some bosch (if i remember correctly) language by the tmc and then fed back to RNS-D.

So in simple terms you need to bypass the tmc module so that your connects2 adapter gets canbus messages and not propiretary bosch ones.

All the manuals to understand complete this conversion are on this forum.

Good luck!

[Laisvydas]

Thank you so much for the detailed information! I wasn’t expecting such a thorough answer, and it’s really appreciated.
So, as I understand it, I just need to locate which wires from the MFSW relay go to the TMC module, then disconnect them and connect them directly to the adapter - and that should make the steering wheel controls work with the head unit.

Thanks again for the great advice! I’ll give it a try once the weather warms up and the season kicks off. Looking forward to getting this done!

[MikkiJayne]

You don't need to trace wires and they are utterly buried in the harness behind the hvac box anyway. The CAN in and out on the TMC are in the same connector. Pop the cluster out and its right back there. You can join the in and out together (check the wiring diagrams in the electrical section for the right colours for CAN-H and CAN-L - don't mix those up) and then the proper CAN from the MSFW module will be present in the connectors at the head unit and you can connect the adapter to them. You can remove the TMC module completely and just join the two antenna connectors together, and tape up the power wires.