Citroen C5 Remote Locking Problem

Sounds familiar! I had similar symptoms on my old Opel Astra. The central locking was acting up, and the car was complaining about key recognition. Have you checked the antenna cable connections for corrosion or damage?

You mentioned cable connections - where exactly are these connections located? And which antenna are you referring to in particular?

On my Astra, the antenna connection was near the bumper, behind the wheel arch liner. I'm not sure about the C5, but it's probably a similar setup. Given your symptoms and the antenna reference, I'd suggest having a workshop take a look. It could save you a lot of time and headache.

Thanks for the advice. It was indeed a defective cable or plug connection to the vehicle antenna, just as suspected. Repair cost me 95€. Now everything works as expected again!