Seat Arosa audio and navigation failure

Sounds like a MOST bus issue alright. The lack of audio and navigation points to that. The MOST bus is a fiber optic network that connects the audio system, navigation, and other multimedia components. When one of the control units on the bus fails, it can disrupt the entire system. Have you tried scanning the car for error codes? That might help pinpoint which control unit is causing the problem. Also, sometimes a loose connection on one of the fiber optic cables can cause issues. Worth checking if you can easily access any of them.

Thanks! Error memory definitely has something stored. I've got some basic car diagnostics tools, but nothing that goes super deep into car electronics. I saw something about 'automotive protocol' in the error description. Is there any way to figure out which control unit is failing without some crazy expensive equipment?

Yeah, without professional car diagnostics equipment, figuring out the exact control unit is tough. 'Automotive protocol' likely refers to the communication standard used on the MOST bus. Unfortunately, tracing faults in fiber optics and diagnosing specific control unit failures usually requires specialized tools. Given the symptoms and the error code, it does strongly suggest a defective control unit. Honestly, you're probably best off taking it to a workshop that specializes in car electronics. They can properly diagnose the issue and replace the faulty unit. Be prepared though, these types of repairs can get pricey.

Thanks so much for the help! I took it to a garage that specializes in car electronics. They confirmed it was a faulty control unit on the MOST bus. Ouch, 1000€ later and everything is working again. Expensive, but at least my tunes are back!