XT6 Audio & Nav System Failure: MOST Bus Breakdown

Had exactly this issue on my 2019 XT5, which uses a similar data transmission setup. I have some hands-on experience with automotive electronics, but still needed professional help for this one. The car diagnostics confirmed problems with the bus network communication, specifically a faulty control module in the MOST bus system. These automotive protocol issues can be tricky because one bad component can disrupt the entire bus system. The repair process involved: Complete system scan, Testing individual control units, Replacing the defective module, Reprogramming the new unit, Final system validation Total repair cost was 1000€ including parts and labor. The workshop had to use specialized diagnostic equipment to pinpoint the exact failing component in the bus network. Before offering more specific advice: Have you checked if all fuses are intact? Did this start suddenly or gradually? Are there any other electrical issues? Which exact trim level is your XT6? This information would help determine if your issue matches what I experienced with my XT5s bus system failure.

Last service was at 189000 KM. The fuses are all good and it started quite suddenly during normal operation. Having read through multiple technical bulletins, I suspect there might be a break in the fiber optics ring that connects the audio components to the main control unit. The audio symptoms match what others describe, even the backup camera display works fine, just no sound output through any speakers or warning chimes. The car electronics seem otherwise normal except for the entertainment functions. Looking for a complete repair process and cost estimate before booking a workshop appointment. Right now leaning towards having the entire bus network checked since a failure in one control unit could affect the whole chain. Anyone with actual repair experience on the 2021 XT6 entertainment system would be especially helpful.

Thanks for those details, they really help confirm my earlier diagnosis. Your symptoms are nearly identical to what I experienced on my XT5, particularly the part about the backup camera working but having no audio output. This is a classic sign of MOST bus system failure affecting the audio control unit. The fiber optic ring issue you mentioned is exactly what my workshop found. In my case, one faulty control unit was disrupting the entire bus network. The car electronics outside the entertainment system worked fine, just like yours. Since you mentioned checking technical bulletins, there was actually a known issue with these control units in our model years. When they replaced mine, the workshop used an updated version that resolved the original design flaw. Final repair breakdown from my experience: Diagnostic testing: 180€, Control unit replacement: 650€, Programming: 170€ Total came to 1000€, which seems to be the average cost for this type of audio system repair. The good news is that once fixed, the issue hasnt returned in over a year of driving. Given the matching symptoms and the fact that the XT6 uses the same basic bus system architecture as my XT5, I strongly recommend having the MOST bus diagnostics done as soon as possible to prevent any potential cascade failures in the system.

Thank you all for the detailed input. This really helps validate my suspicions about the MOST bus system being the culprit. The matching symptoms between our vehicles and the specific mention of fiber optic ring issues gives me a much clearer picture of what to expect. Based on the shared repair experiences, especially regarding the data transmission problems, I will schedule the diagnostic testing. The 1000€ total repair cost seems reasonable given the complexity of the audio system and control unit replacement needed. Quick follow up before I book the appointment: did any of you experience recurring issues after the repair? Also wondering if there were any temporary workarounds for the audio system while waiting for the repair slot? The silence during my commute is getting pretty annoying, but I want to ensure I get this fixed properly rather than attempting any quick fixes that might cause more damage to the bus network. Will update the thread once I have the workshop findings. This could help others dealing with similar control unit failures in their entertainment systems.