T-Roc Media System Dead: MOST Bus Connection Failure

I had almost identical issues with my 2017 T-Cross, and having some experience with car electronics, I initially thought it was just a simple head unit problem. The symptoms were exactly the same, complete failure of the audio system and all connected features. The data transmission through the MOST bus was completely interrupted, affecting the entire multimedia setup. After multiple basic diagnostics failed, I took it to a specialized workshop. They found a defective control unit in the fiber optics network that was disrupting the bus network communication. The whole diagnostic process took about 4 hours because they had to test each component in the MOST bus chain individually. The repair involved replacing the faulty control unit and reconfiguring the entire system. Total cost was 1000€, including parts and labor. Since then, the audio system has worked flawlessly. Before suggesting specific solutions, could you share: Have you performed any diagnostic scans? Which error codes are stored in the control unit? Did this issue start suddenly or gradually? Are there any other electrical issues in your car? This information would help determine if your issue matches what I experienced and provide more targeted advice.

Thanks for your detailed input. My latest service was 2 weeks ago, they did not detect any issues. My automotive protocol scan shows error code 03657 appearing repeatedly. The issue started quite suddenly after a heavy rainfall last week. I noticed other minor electrical glitches too, the parking sensors sometimes give false readings. I checked the car diagnostics data through a basic OBD reader but could not get a clear picture of the data transmission issues. Planning to take it to a workshop soon, but wanted to get some community insights first to better understand the potential problems with the bus system communication. Would it make sense to first check the fiber optic connections before replacing any control units? Looking for the most cost-effective approach here.

Based on what you describe, your situation sounds very similar to mine. The error code 03657 and the symptoms following rainfall strongly point toward a moisture-related MOST bus failure, which matches my experience exactly. In my case, checking the fiber optics connections first actually saved money in the long run. The workshop found water ingress near one of the main fiber optic connectors, causing signal interruption in the MOST bus network. The moisture had created corrosion in the connection points, leading to intermittent car diagnostics issues, including those unusual parking sensor malfunctions you mentioned. The initial inspection of the fiber optics system cost 150€, which was much cheaper than blindly replacing control units. They found the damaged connector, dried the area, and replaced just the affected fiber optic segment. This fixed both the audio system issues and the other electrical glitches. Complete repair breakdown from my experience: Diagnostic scan and fiber optics inspection: 150€, Replacement of damaged fiber segment: 200€, Labor for drying and sealing connections: 180€, System recalibration: 120€ Total came to 650€, significantly less than a full control unit replacement. The car electronics have worked perfectly since then, with no audio system issues for over a year now. Definitely have them trace the fiber optic connections first, particularly around areas where water might collect. This targeted approach could save you considerable money compared to component replacement.

Thanks for breaking down your repair experience. Your suggestion about checking the fiber optics first makes a lot of sense, especially given the timing with the rainfall. I checked with another mechanic who quoted 900€ just for replacing the control unit, so starting with the fiber optics inspection at 150€ seems like a smart approach. The error code and symptoms are identical to what you experienced, and the data transmission issues affecting multiple systems definitely suggests a MOST bus communication problem rather than individual component failures. I will schedule the fiber optics inspection next week. My car diagnostics also showed some voltage fluctuations that could be related to the moisture problem you mentioned. The intermittent nature of the parking sensor issues also matches your experience with the corroded connections. Will update once I get the results from the workshop inspection. Really appreciate the detailed cost breakdown and technical explanation, helps a lot in understanding what to expect during the repair process.