JTIS has a pinpoint test for the sensor. You have to unplug it to test, which is the hard part in my opinion. The procedure is on my other computer which is not at hand.

 

Have you checked the wires on the connector on the O2 sensor and those that go into the wiring harness connector that the O2 sensor connects too, check to see if they are connected?
I replaced my o2 sensor and still got check code P1647. Turns out on the wiring harness side, on that connector, I had a wire PULLED OUT. You may want to check the connectors, make sure all the wires are pushed in. I totally missed the brown wire that came out, prob didn't even have to replace the damn sensor if I had looked closer. I suspect when I pulled my octopus hose out it tugged on that connector and prob pulled that wire off the connector but still stayed in the connector grommet (wires are run through a grommet in the connectors) till I got to really fiddling with it and pulled the wire all the way out.

 

When I replaced my sensor for upstream o2, I made sure the wiring matched the orig one that was in the car, black and blue wire and two whites on the o2 sensor wiring setup on my 03! There are multi wires/colors on the connector the O2 one connects too.

 

to take it off, get a o2 sensor socket set from any parts place, rent it or by it. 7/8 is the size. I used the small on and small ratchet drive, you can get to it without taking out anything to make room though it is tight quarters.

 

Thanks for that info i will check the wiring.

I found the thread that has an easy way to remove the sensor

https://www.jaguarforums.com/forum/xk8-xkr-17/very-easy-upstream-oxygen-sensor-replacement-115991/

 

Do you know which fuse to check for P1647? Could you elaborate on the potential damage to car if not fixed; there is very little noticeable decrease in performance, other than the engine seems to idle a tiny bit rougher. Car still leaps as before when pedal is smashed...