Audi RS4's Dead Infotainment Points to MOST Bus Failure

I had a similar issue with my 2014 RS6 last year. Have some experience working on car electronics and audio systems, but this was definitely beyond basic DIY fixes. The symptoms matched exactly, complete infotainment failure and multiple control unit errors. After initial diagnosis showed MOST bus network communication problems, I took it to a specialist workshop. They found a defective control unit that was disrupting the entire fiber optic ring. The repair involved: Complete diagnostic scan of all control units, Testing the MOST bus network integrity, Replacing the faulty control unit, Reprogramming and coding the new unit, Final systems check Total cost was 1000 Euro and took about 2 days to complete. The automotive protocol testing equipment they used was quite specialized, so this definitely needed professional intervention. Could you share: Any specific error codes showing up? Does the issue happen constantly or intermittently? Have you noticed any correlation with temperature or weather conditions? Were there any modifications done to the audio system previously? This information would help determine if your case is similar and might need the same approach.

Thanks for the helpful details on the bus system repair. Latest service was at 52000km and the issue started shortly after. I ran additional car diagnostics and found error code 03276 consistently appearing. The problem is definitely constant rather than intermittent. The fiber optics connection seems completely dead with no signal passing through according to my scan tool. Temperature and weather dont appear to affect it. Car is completely stock with no audio modifications. Thinking I might need that specialized testing equipment you mentioned to properly trace the fault in the optical ring.

Thanks for the additional details. That error code 03276 is a classic indicator of a data transmission fault in the MOST bus network, which matches exactly what I encountered with my RS6. Based on the timing after your service, I suspect they might have accidentally damaged the fiber optic cable during some other work. My repair also started with consistent error codes and complete signal loss in the bus system. The fact that your issue is constant rather than intermittent actually makes diagnosis easier, intermittent faults in the control unit network are much harder to trace. A few observations from my experience: Complete signal loss often points to a physical break in the fiber optics rather than a control unit failure, Post-service timing suggests possible accidental damage during maintenance, Stock system eliminates aftermarket modifications as potential causes The specialized testing equipment used on my car included a MOST protocol analyzer and fiber optic signal tester. Without these tools, the workshop would have needed to replace components through trial and error. Strongly recommend having a specialist workshop check the entire fiber optic ring with proper diagnostic equipment. Could save significant time and money compared to replacing parts speculatively.

The feedback about checking for physical damage in the fiber optics makes a lot of sense, especially given the timing after the service. I checked my workshop records and they did remove several interior panels to access the transmission, which could have impacted the bus network cabling. The specialized testing equipment seems crucial here, my basic scan tool clearly isnt enough for proper car diagnostics of the fiber optic system. I contacted a workshop that specializes in car electronics and they quoted 2 hours labor just for the initial control unit testing and MOST network analysis. Since the symptoms match your case so closely, including the complete signal loss in the audio system, I will proceed with the professional diagnosis. The constant nature of the fault should make it easier for them to trace using their protocol testing equipment. Will update once they identify whether its a damaged cable or faulty control unit causing the bus network failure.