Peugeot 508 electrical malfunctions navigation failure

Sounds like a potential software issue. The error memory and electrical gremlins point that way. "Control unit" refers to the car's central computer, which manages many systems. When it comes to software problems, did you try a software reset? Also, does the error message point to a specific module or system?

Thanks for the info. I haven't tried a software reset myself, as I'm a bit wary of messing things up further. The error message doesn't specify a particular module, just a general 'implausible programming' error. Could this be fixed with a software refresh or do I need a new control unit?

An 'implausible programming' error often means the control unit's software is corrupted. It's unlikely a full replacement is needed yet. A software refresh or reprogramming is usually sufficient. But in that case you need professional help from a workshop. So better take it there, before you mess things up even more.

Thanks for confirming my suspicions and the advice! I took it to a workshop, and they were able to reprogram the control unit. Cost me 240€, which I think is reasonable. Everything seems to be working fine now.