I have seen many questions across the internet about SD cards showing as unreadable in an Audi when I had the problem myself.

Most went unanswered but when I found answered questions, they only pointed at how the card should be formatted (as per Audi manuals) and this never solved my problem.
In short you have to format on a PC!

Here are the steps to my example.

Audi require that:-
The SD or MMC card is formatted in MS DOS FAT16 or FAT32.
Capacity of card to be 4 GB (this may be superseded and newer models may accept larger capacity cards)
The media is MP3 or WMA (version 7,8 or 9) format.
Play lists need to be m3u format (iTunes is capable of this).
ID3 tags/ WMA tags should be version 1.1,2.3/version 7,8 or 9 respectively.note: These are tags that allow the song titles and artist e.t.c. to show on the cars display. Again iTunes can do this.
So after all this had been taken care of, my card (which had previously worked in the car) still came up as unreadable.


The Disc utility on a mac for formatting does have a FAT32 option which I chose. Then when I looked at the card properties it tells you it is formatted in FAT32.
The card worked on the mac and a macbook.
I rang apple.
The cause turned out to be....
I was formatting the card on a Mac!

They say, something in the way apple and windows format FAT32 is different and an SD card cannot understand it.
You can use a mac to erase and add files to the card and it will work.
But
The Format needs to be done on windows based PC for the car MMI to understand it.

I tried what they said and found it cured my problem. Hopefully that will clear it up for others with the same issue.
Incidentally, it got me wondering what use the FAT32 format was on the mac disc utility option was.
The apple advisor told me the issue was only on SD cards. Therefore, if you have a portable hard drive and formatted it on a mac as FAT32 it would be universally understood by other computers.

Regards
Kojak
Who luvs ya baby!