Dead Audio & Nav in S6: MOST Bus Failure Suspected

The symptoms match exactly what happened with my 2019 Audi A6 50 TDI. The control unit failure in the MOST bus system caused a complete blackout of both audio system and navigation components. The automotive protocol diagnostics revealed multiple communication errors between modules. The root cause was a defective fiber optic ring controller, which affected the entire MOST bus network. This required specialized diagnostic equipment to properly identify the failing component. The repair involved replacing the main control unit and reprogramming the entire infotainment system. This is not a typical DIY job as it requires specific coding tools and expertise in MOST bus diagnostics. The repair was quite serious since the MOST bus serves as the backbone for all entertainment and navigation functions. The fix required official dealer equipment to properly integrate the new control unit into the vehicle network. While component replacement is straightforward, the programming and adaptation procedures are complex and require manufacturer-specific tools. Based on the symptoms described, having questionable work done previously could indeed have damaged the fiber optic connections or control units in the MOST bus network. Recommend getting this diagnosed at an authorized service center with proper diagnostic capabilities.

Thanks for sharing that detailed repair experience. I had the exact same symptoms on my S6 but wasnt sure if the car electronics failure was related to MOST bus issues or just a faulty head unit. The car diagnostics also pointed to multiple communication errors. Did you remember roughly how much the repair cost at the dealer? Im especially curious about the control unit price and labor since my local shop quoted quite high. Also, has everything worked perfectly with your audio system and other connected features since the fix?

Got back to my A6 from the dealer yesterday. The MOST bus fault causing our shared communication problems was fixed by replacing a faulty control unit in the data transmission system. Total repair came to 1000 Euro including parts and labor. All infotainment functions are now working flawlessly. The audio system, navigation and other connected features through the bus network are back to normal operation. The specialized automotive protocol diagnostics they used pinpointed the exact component failure in the bus system. Your local shop quote might be high but given the complexity of MOST bus repairs and need for specific programming tools, pricing can vary. The critical part is ensuring whoever does the work has proper diagnostic equipment for MOST bus systems. Getting it done right the first time saves headaches later. My suggestion based on this experience would be to proceed with the repair despite the cost. These bus network issues tend to worsen over time if left unaddressed.

Thanks everyone for the helpful responses. Just wanted to update on my S6 situation. Took it to the dealer after seeing the feedback here about needing specialized MOST bus diagnostics. Turns out the previous shop had damaged the fiber optic connections while doing unrelated work. The repair involved replacing the main control unit and reprogramming the entire bus network. Total cost was 1200 Euro which included the new unit, programming, and labor. More than I wanted to spend but the automotive protocol diagnostic equipment they used confirmed it was necessary. Been driving for a week now and the bus system is working perfectly. All audio, navigation and connected features are back to normal. Definitely learned my lesson about letting non-specialized shops work on complex vehicle electronics. The dealer technicians showed me the damaged components and explained how the MOST bus network operates, which helped understand why the repair was so involved. Really appreciate the advice that helped point me in the right direction for fixing this issue properly.