I bought a used Volvo V40 (2002). It worked great for about two weeks, after which the central locking stopped working. The FOB doesn't do anything, and each door has to be locked and unlocked separately like back in the old days. The worst thing is that the passenger-side doors are completely locked and I can't open them at all.
Anyway, I suspect the problem lies either in the relay or the central locking control unit. How would I know which one is it? I already checked the fuses and they're all OK.
I know where the control unit is located (under the CD player) and is seemingly easy to take out and replace, but they're not really available anywhere. I personally suspect the relay more since there's no relay clicking when the locks are used. However, I don't know which relay it is or where it's located. I also couldn't find any "central locking relays" in the local shop's catalog - I hope it's a standard relay you can buy anywhere.