Mini Cabrio Passenger Seat Issue

Is the error always present, or does it come and go? Have you checked the seat wiring connectors under the car seats themselves? They can sometimes get loose or corroded. Also, does the driver's side seat adjustment work fine?

Good shout on the connectors. Where exactly under the car seats should I be looking, and what am I looking for? Is there a specific pin in the connector known to cause trouble?

The connectors are directly under the seat, accessible by reaching underneath. Look for any that seem loose, disconnected, or show signs of corrosion white or green deposits. As for specific pins, not really sure, but a bad battery can definitely cause weird electrical issues with car seats. If you're not comfortable poking around, a workshop visit is probably best.

You were spot on. Dropped the Mini at the shop. They confirmed it was a dodgy battery causing the passenger seat to throw a fit. New battery and seat wiring check later, all good. 290€ lighter, but at least my passenger won't be stuck in one position. Cheers!