Hello everyone,

I just wanted to see if anyone can confirm what I think is true after reviewing some of the wiring diagrams on my car. I have an 09 A4 Premium with MMI, BT, Sirius.

It looks like the Digital Sound System Control Module (J525) has a CAN bus input that carries all signals including the audio and there are no line level inputs from the head unit.

If this is correct then in order to install a subwoofer my best option is to drive down the speaker level subwoofer to a line level signal with an adjustable resistor bridge. Is this correct or am I misinterpretting the diagrams?

 

Hi MH,
From your title you have Symphony radio, is that written above the CD slot?
If so, you don't have MMI as far as reading the technical documentation goes. As far as I can determine, Symphony is listed as "Radio Basic Plus" in the docs.
I am also pretty sure that CAN bus is not used for carrying audio signals.
The wiring diagrams that I found (ELSAWIN) show four pages where the relationship between "R" (your radio) and J525 (digital sound system control module).
On the first page, yes, it looks like everything must travel between the two via CAN, but if you look at the next two pages there are 8 more wires connecting the two units, which I believe to be audio connections. Can't tell which are which though so yo umay still have to use the outgoing speaker connections to tap into for your sub. Those same pages show all of the speaker connections...

 

Okay, I found everything on my DVD. I have the "Radio with Soundsystem Standard". I now see that CAN is for infotainment only.

For anyone else who is interested in removing the factory sub and adding your own here is the pin and wire color to line level table for the Radio connector T8k and the Digital Sound System Control Module connector T32h:

RADIO--DSSCM
PIN-----PIN------COLOR--------------SIGNAL
1-------23-------WHITE/YELLOW-----RIGHT REAR +
4-------24-------GREEN/BLUE--------LEFT REAR +
2-------25-------RED/GREY----------RIGHT FRONT +
3-------26-------GREEN/BLACK-------LEFT FRONT +

5-------28-------GREEN/YELLOW-----RIGHT REAR -
8-------29-------WHITE/BLUE--------LEFT REAR -
6-------30-------BROWN/GREY-------RIGHT FRONT -
7-------31-------WHITE/BLACK-------LEFT FRONT -
---------1-------WHITE/RED---------12VDC +

I have not verified that the power source for the DSSCM is switched but it seems extremely likely.

There is also a nice ground lug just to the right of the DSSCM so there is no need to scratch any paint off to get a good ground for your amp.

There you have it. The only wiring required to the trunk is your fused amp power from the battery.

I see that this is really a DIY post so I will make a new thread over there when I have verified everything and my install is complete with photos.

Thanks for the reply!