RCZ Passenger Seat Electric Fault

It sounds like an electrical issue, possibly related to the seat wiring or the seat control module. Given the car's age, have you considered the battery's condition? A discharged or defective battery can sometimes cause electrical gremlins. Check the battery's voltage and health before digging into the seat wiring. Are other electrical components behaving strangely, or is it just the passenger seat?

I haven't explicitly tested the battery's voltage, but the car starts fine, and I haven't noticed other electrical issues. But I know a battery can seem functional while having reduced capacity. Could a slightly weakened battery really cause a completely inoperable seat adjustment? How can I know if the battery is the problem before I start checking the seat wiring?

Even if the car starts normally, a slightly weakened battery, especially in a vehicle with as many electronic components as the RCZ, can cause issues with specific systems. The seat control module might be sensitive to voltage fluctuations. It's not a guarantee, but it's plausible. I'd suggest having the battery professionally tested under load. If the battery checks out, start checking the seat wiring and connectors. Given the complexity, you might want to consult a workshop.

I took the car to the workshop, and they diagnosed a defective battery causing the problem. Repair cost 290€. Thanks again for your help.