I have a 2002 XK8 Convertible.
just wanted to post a success story rather than an issue.
My car had a rotten passive sounder. Which I removed and coped with locking via the key and having to get the key in the ignition when it was unlocked.
Recently tried putting the sounder back in. Checked the relevant fuse which had blown. Tried reprogramming the fobs, car would go into learning mode but wouldn’t respond to fobs. Checked the security module antenna which had been caught by the battery in the boot but was still ok. Still no joy with the fobs. Undid the bolts holding the boot fuse box so I could get at the security module. I removed the module and with a couple of screw drivers managed to remove the cover without breaking anything.
no obvious damage. To the antennae pcb or the main one. Good friend of mine suggested cleaning the board with some contact cleaner which I did with some cotton buds. It wasn’t very dirty but boards can get oxidation on them which stops them working.
I put everything back together, back in to learning mode and the vehicle suddenly started responding to the fobs, and the central locking was restored.
Definitely worth trying this if all else has failed. It’s not as big a job as it sounds, just be careful when handling the circuit boards and don’t give up on the sounder even if the contained circuit board looks completely corroded from the rechargeable batteries leaking.