2008 XJ Super V8 with check engine light and the following codes: P0171, P0174, P0420, U0167, P2601. Where do I start?

 

I'd start in the sub-forum dedicated to your model.

https://www.jaguarforums.com/forum/x...-x350-x358-28/

 

First off you will have a much better chance at getting answers to your problems if you post in the X350 forum since the members there have like vehicles.
https://www.jaguarforums.com/forum/x...-x350-x358-28/

Now to your problems.
Codes P0171 and P0174 indicate lean conditions left and right bank. Somewhere you have a good size vacuum leak. I would start with a good inspection of the snorkel running between the MAF and the throttle body. They are known to crack in the corrugated area on the bottom and would cause a vacuum leak.
The P420 is catalytic convertor out of range. This would probably be fixed once the vacuum leak is fixed.
The U0167 is a loss of communication between the ECM and the immobilizer this is possibly a result of the P2601. P2601 is a failure of the inter-cooler pump. It could be a blown fuse or a bad pump. Failure would cause increased heat soak and the heat could be creating the loss of communications between the modules.
Others in the X350 forum may be have additional ideas.

 

Thanks very much! I appreciate your quick response .