Vauxhall Vectra MOST Bus Failure

MOST bus issues can be a real pain. Since everything on that loop is affected, you're right to suspect a control unit. Have you tried any basic diagnostics? Like checking the power supply and ground connections to the head unit and other modules on the MOST bus? A bad power connection can sometimes cause these kinds of widespread failures.

Yeah, I checked the power and grounds to the head unit itself, and they seem fine. I haven't gone through every single module on the bus though – that’s a lot of digging. Is there a common culprit on these Vectras that I should check first, or is it really just a case of systematically testing everything?

Unfortunately, there isn't one common point of failure that I'm aware of for the Vectra MOST bus. Given the symptoms and your checks so far, it really does sound like a deeper dive is needed. At this point, unless you have access to some advanced diagnostic tools and the wiring diagrams, it might be worth taking it to a workshop with experience in car electronics and diagnostics. A proper scan with a Vauxhall-specific tool could pinpoint the faulty module much faster.

Thanks for the advice. Sounds like I'm in for a headache. I'll take it to a shop. They reckon about 1000€ to fix it... ouch!