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Tech Article

Audi C5 A6 Symphony Sound System (Stereo unit, Radio) Battery Swap and Unlock Code

Last Updated: 04/11/2017
Parts Group: Stereo sound system / radio main unit
I recently bought another Audi C5 A6 with the Audi Symphony Sound System (Stereo unit, Radio). The radio was working just fine when I bought the car, but I don’t have the radio unlock code.

The car battery was iffy yet I was wary of replacing it because I was concerned that the radio would lock itself and that I, lacking a radio code, would then be unable to unlock it. I considered finagling something with a pair of jumper cables and two batteries in parallel, so that the car would continue to have power while I swapped out the old, not-so-happy battery.

Then, someone wise explained to me that the radio code synchronizes the car’s eletronic control unit with the radio, and that these are stored in a way that survives the loss of general battery power. As she explained it, when the car has power again, then as long as it still has the same radio as before, I would not need to re-enter the radio code.

Not without some trepidation, I unhooked the battery and removed it, then installed a fresh one. I turned the radio on. It worked fine ... without requiring me to re-enter a code. That would seem to prove her point.

Then, we swapped in another radio, entered its code, and it worked. Then, we removed the battery for a few minutes ... and the radio required a radio code yet again. The next best hypothesis is that these radios have an internal battery that remembers the code for a while, if that internal battery is working.

My tech looked into it, and she learned that the radios came with an earlier control set that requires the radio code every time the main battery is disconnected, but there is also a later control set that's smart enough to pair itself with the electronic control unit and then even if the main battery is removed, then as long as it's the same electronic control unit, a new radio code is not required. Better!
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