I heard that little fan coming on at idles and I chose to ignore it...

However I did order a new thermostat from Atlantic British so I have it on the shelf.

Right before the needle spiked (it didn't go all the way, maybe 3/4ths before I cut it off) the check engine light came on and I havent had the chance to pull the codes.

Any ideas on possibilities? She is running smooth btw.

 

Code P1173

 

P1173 Downstream fuel trim malfunction (bank 2) Front sensor aged - rear HO2S adaption too lean/too rich RH bank

http://www.canobd2.com describes the error as:
P1173 - Land Rover - Lambda sensor aging tv bank 2\nDrive cycle C:Signal out of range - above maximum.\n

Before ordering o2 sensors check the PCV for cracks or restrictions. Once you confirm there are no issues proceed to test the o2's.