I am still getting SES lights even after O2 sensor install:

P0150 O2 Sensor Circuit (Bank 2 Sensor 1)
P0174 System Too Lean (Bank 2)
P1174 System Too Lean - Banks 1 and 2 (Suspect HO2S) or Cam Sensor

Just FYI, both pre cat sensors were replaced by the PO recently and I just replaced the two post cat sensors. WTH.

 

I had the exact same codes, put a new Bosch O2 sensor in and still had the codes. The new sensor was dead on arrival. Bought another new one, installed, and fixed.

 

You are talking about the pre-cat sensors correct? Did you just replace the passenger side sensor (bank 2) or did you do both?

 

Check the O2 plug to make sure it is snapped in all the way and there is no oil that has dripped down from above onto the plug.

For the other codes I would start off that search with a smoke test for a vacuum leak. Here is a DIY smoke test thread I made to track down small vac leaks. I have used it twice to fix lean codes I was getting. First time was a hose clamp not tight enough where the intake tube connects to the throttle body, the second time was old lower o-ring on my injector leaking.
https://landroverforums.com/forum/di...s-cigar-54235/

 

Since the PO put those sensors in - so what?
Replace them!!!
Haha, depends how long that guy was the PO.

On my 2001 Discovery the PO replaced both front O2's I think.
And I ended up replacing 1 of those under my tenure.
That ended up fine and the code left.

Check codes with
http://enginecodemaster.com