Citroen C6 passenger seat failure

Sounds familiar! I had a similar issue with my old BMW 5 series. The error memory kept logging errors, and the seat wouldn’t budge. Was your battery recently drained or anything? That was my problem.

Actually, the car did sit for a couple of weeks while I was on vacation. Could a weak battery really cause the seat motor to fail like that?

Yep, that was exactly it for me. The BMW's electronics are super sensitive. A low battery throws everything off. I'd get your battery tested. If it's weak, replacing it might solve the seat issue. If not, then I'd head to a workshop.

Turns out the battery was the culprit. A new battery and a reset, and the seat's working perfectly again. Cost me 290€ at the shop. Appreciate the help!