I've changed the 2 pcs of 2016 lithium button cells on the remote keyfob, but there is still no response from the XK8, and have been resorting to manual locking with key.

How should I proceed to diagnose which module(s) or the remote keyfob is at fault?

TIA

 

I'm not being a smart aleck but did you make sure that the polarity matched the existing configuration when you installed the new batteries? Will the remote unlock the boot? If the batteries are correct and the boot won't open then you will need to reprogram the remote. A quick advanced search will give you the procedure. If you have only one remote you will have to program it 5 times if you have 2 remotes then only the second will need to be programmed 4 times. You have to let the car think you have all 5 remotes.

 

I am completely baffled. What do you mean by "let the car think you have all 5 remotes"? I believe new Jags only come with 2 remotes.

Why do I have to reprogram the remote(s) in the first place?

 

The remote is not what is programmed the security module is what is programmed but I am not sure you need to do that yet. Take a look at the attached link. It will show you how to clean the remote. Try that first before digging to the problem.

Link to remote cleaning JagRepair.com - Jaguar Repair Information Resource