Audi S5 MOST Bus Failure Kills Audio & Navigation

I faced nearly identical issues with my 2018 Audi S4 last year. Having some experience with audio system troubleshooting, I initially tried basic fixes like system resets, but the symptoms persisted. The main problem was a defective control unit in the MOST bus system, which handles data transmission between entertainment components. The diagnostic scan showed communication errors across the bus network, affecting both audio output and navigation functions. The repair required: Complete diagnostic of the fiber optic network, Replacement of a faulty control unit, Reprogramming of the new unit, Testing all affected systems Total repair cost was 1000 Euro, and the workshop needed 2 days to complete everything. Since then, all entertainment functions have worked flawlessly. Could you share: Whether your diagnostic tool shows specific error codes? If the issue appeared suddenly or developed gradually? Whether you notice any intermittent functionality? If any recent work was done on the electrical systems? This information would help determine if your issue matches the same bus system failure pattern I experienced.

Last service was at 48000 KM and car diagnostics showed error code U0415. Initially thought it might be a simple system glitch but when checking the service history documentation, noticed similar intermittent issues started appearing 2 months ago. Started with occasional audio system drops before complete failure. The fiber optics network diagnostic confirmed my suspicions about the MOST bus connection. Currently waiting on several quotes as control unit replacement seems inevitable based on data transmission errors showing up consistently. A certified workshop quoted repair time between 8-12 hours.

Thanks for the error code details. The U0415 code matches exactly what I experienced with my Audi S4, it specifically indicates car electronics communication problems on the MOST bus network. The progression of your symptoms through intermittent audio failures to complete system shutdown follows the same pattern I encountered. When the control unit starts failing, the data transmission between components becomes increasingly unreliable before total failure occurs. The 8-12 hour repair estimate seems a bit high compared to my experience. The automotive protocol diagnostics and control unit replacement took about 6 hours in total at my workshop. Unless they found additional bus network issues during testing, you might want to get another quote. Two recommendations based on my repair experience: Request a full fiber optic ring test before parts replacement, Ensure the workshop uses OEM parts for the control unit replacement The intermittent issues you mentioned developing over 2 months are a telltale sign of gradual MOST bus degradation, very similar to what led to my complete system failure.

I really appreciate all the detailed feedback. After checking three different workshops, I found significant variations in repair quotes and timeframes. Based on the shared experiences here, I will proceed with the repair at a workshop that specifically mentioned performing the fiber optic ring test first. Their diagnostic approach aligns with what worked for others facing similar car electronics issues. The automotive protocol diagnostic results they provided match the U0415 error code pattern, confirming the bus network failure. Their quote of 850 Euro for parts and labor seems reasonable compared to other experiences shared. They estimated 6-8 hours for the complete repair, including testing all affected systems. Going forward with the control unit replacement next week. Will update on the results after repair completion, as this information could help others dealing with similar MOST bus communication failures in their vehicles.