Electrical Mavens Needed: A friendly cab driver reversed jumper cables when jump starting a 2001 A8 that was on loan to a friend. Now the Symphony Bose radio will not power up and get no read out from the scanner, it shows no error codes just says "not communicating". Checked the fuses in passenger foot rest, in trunk above battery and fuse box in plenum near CMU, not one blown fuse anywhere. The battery is ok takes a full charge. Have I missed any fuse locations? Are there any more places to look for electrical damage as to fuses or relays? How do you deal with no readout from the scanner?

 

There is a fuse located behind the radio. Odds are you fried the radio or the radios fuse. Only way to tell is pull it out and check. Hope this helps.

 

Thanks pa4ul for your help. I used four radio removal keys purchased from toolsource.com to effortlessly remove the radio and found a 7.5 amp blown fuse. The radio works fine with a new fuse.
The more critical problem, after the reversed battery cables, is that the CMU, the car computer is not communicating with a scanner that used to read codes for everything. I replaced both catalytic convertors and all oxygen sensors and get no reading from the CMU for that or any thing else. In the watertight case, in the plenum area, the CMU has a fuse bus with four fuses and a relay(I think) all the fuses are ok but the CMU????
Are there any more fuses that protect the CMU somewhere? Is there a way to test CMU independent of the scanner plug under the steering wheel? Attached is a picture of the CMU and fuse bus. Assuming the worst that I shorted out, will any Audi dealership repair facility be able to tell how the CMU was damaged? Is there any way for them to do forensic probing of the CMU or will it simply be a unit that malfunctioned, cause unknown?