VW Phaeton MOST Bus: Complete Infotainment Failure Fix

I faced a similar issue with my 2007 VW Touareg V6 TDI, which shares many electronic components with the Phaeton. After dealing with car electronics for several years, I can share some relevant experience. The MOST bus network failure in my case also caused a complete shutdown of the audio system and navigation. The workshop first performed comprehensive car diagnostics to isolate the faulty component. They found a defective amplifier control unit that was disrupting the entire optical ring. Initial diagnosis pointed to multiple possible failures, but the systematic testing revealed the specific control unit was not properly transmitting signals through the fiber optic loop. The complete repair, including diagnostics and control unit replacement, cost 1000€. Before suggesting specific solutions for your case, could you provide: Complete diagnostic error codes, Whether the failure occurred suddenly or gradually, If any aftermarket audio components were installed, Whether the issue appears temperature-related (better/worse when cold/hot) These details would help determine if your issue matches the common failure pattern I experienced with the control unit, or if it might be a different component in the MOST bus system causing the communication breakdown.

Thanks for the detailed feedback. Since my last service at 75000km, I noticed the data transmission issues became more frequent. The error codes are identical to what you described, and the failure started gradually over two weeks. The workshop first suspected a loose connection, but after checking the fiber optic connections, they found no visible damage. No aftermarket components were ever installed. The audio system failures seem worse during cold starts, with occasional recovery after the car warms up. The control unit diagnostic you mentioned matches my symptoms perfectly. Did your repair also resolve the cold start issues? My concern is spending 1000€ on parts without certainty of fixing the root cause.

The cold start behavior you describe is exactly what I experienced, it's a classic symptom of a failing control unit in the MOST bus network. In my case, replacing the amplifier control unit completely resolved both the cold start issues and the intermittent data transmission failures. The gradual deterioration pattern, combined with temperature sensitivity, strongly suggests control unit degradation rather than physical fiber damage. The car diagnostics on my Touareg showed similar behavior, partial functionality after warm-up is typical when the control unit starts failing. After the repair, all bus system communications were restored, and the infotainment worked flawlessly regardless of temperature. The 1000€ investment was worthwhile since the systematic diagnosis pinpointed the exact component, avoiding the common mistake of replacing multiple parts. The amplifier control unit replacement resolved: Inconsistent cold start behavior, All communication errors in the bus network, Audio system failures, Navigation system outages Given your identical symptoms and error patterns, I strongly recommend having the workshop focus on testing the amplifier control unit first. This targeted approach should save diagnostic time and prevent unnecessary parts replacement.

Thanks, this feedback is really helpful for moving forward. Based on the matching symptoms and error codes, I'll have my workshop focus on the amplifier control unit first. The similar temperature-related behavior especially convinced me this is likely the same root cause. I'll ask them to run targeted car diagnostics on the control unit before exploring other components in the automotive protocol chain. This should help avoid replacing unrelated parts in the bus network system. I feel much better about potentially spending the 1000€ now that I know it resolved both the cold start and communication issues in a similar case. Will ask my workshop to verify the amplifier control unit status and report back after they complete the diagnosis and repair.