Audi A5 MOST Bus Network Failure Disrupts Infotainment

As an owner of a 2021 Audi A4 who dealt with similar issues, I can share my experience with MOST bus failures. I have some experience working with automotive electronics, but this particular issue required professional intervention. The symptoms were identical, complete infotainment blackout and multiple fault codes related to data transmission interruptions. The fiber optics network in these systems is quite sensitive, and the control unit can fail due to various reasons. In my case, the workshop diagnosed a defective control unit that was disrupting the MOST bus communication. The entire diagnostic and repair process took about 2 days, with the final cost around 1000 Euro. The repair involved replacing the faulty control unit and recoding the system to restore proper data transmission between components. Before you proceed with repairs, could you share: Are there any warning messages displayed? Did the issue occur suddenly or gradually? Have you recently had any work done on the electrical system? Does the problem persist after a complete vehicle restart? This information would help identify if your issue matches the common failure pattern in these automotive protocol systems.

Thanks for sharing your experience. My issue appeared gradually over a few days before total failure. Last service was at 142000 KM and no electrical work was done. After multiple vehicle restarts, the bus network remains unresponsive. The control unit shows error messages related to data transmission failure. No warning messages appeared before the complete system shutdown. Based on the symptoms and fault codes stored in the system, it seems the fiber optic ring in the MOST bus is compromised somewhere. Will contact the workshop to check if they have experience with similar automotive protocol failures.

Based on your description, this definitely aligns with the MOST bus failure I experienced. The gradual onset and complete system shutdown without prior warnings matches the typical failure pattern in the car electronics system. In my repair case, after the workshop completed a thorough car diagnostics scan, they identified a break in the fiber optic ring near one of the amplifier connections. The MOST bus requires a complete data transmission loop, and any interruption can cause total system failure. The repair involved testing each component in the bus network until they located the exact break point. They replaced the damaged fiber optic section and performed a complete system reset to restore communication between all components. A crucial point, make sure the workshop has specialized equipment for MOST bus diagnostics. The repair requires precise tools to test the optical signal strength and identify breaks in the data transmission path. Total repair time for my A4 was around 2 days, and it solved all issues completely. If your symptoms are this similar, you might be looking at a comparable repair scope and cost range of 800-1200 Euro depending on the specific failing component.

Thank you for the detailed follow-up. Your breakdown of the MOST bus repair process is quite helpful. The gradual failure pattern in my audio system does match your experience completely. The car diagnostics data from my initial tests shows similar fiber optic ring issues in the bus network. Given the complexity of data transmission systems in modern vehicles, I agree that finding a workshop with proper diagnostic equipment is crucial. I will contact the dealer tomorrow to verify they have experience with automotive protocol repairs, particularly MOST bus failures in car electronics. The repair cost range you mentioned helps set realistic expectations for the work needed. Looking at the complete failure pattern and stored fault codes, I am now fairly confident this is a fiber optic ring issue rather than a control unit problem. Will update the forum once the repair is completed to help others who might face similar issues with their infotainment system.