My check engine light flickered on and off a few times last week during a trip I took. Waited till it came on again and had them read. Came up with the three codes above. I believe they are O2 senors and the engine is running lean. Should new O2 senors make these go away? Do I need all four of them and if I do is there a certain brand anyone recommends. Truck has 90,000 miles on it and I am also trying to track down a ticking noise in another post so I will have the oil pressure tested later this week as well.
Andrew

 

I would replace all four 02 sensors at 90K. They are available at AutoZone & Advanced auto parts.

15175 Bosch Front (upstream) $76 each at Advanced
15630 Bosch Rear (downstream) $68 each at AutoZone

I would get this OEM crowsfoot socket to remove the 2 fronts. Rear can be removed with an adjustable wrench. Spray with penitrant oil the night before.
http://toolsandmore.us/oem25249-oxyg...hcrowfoot.aspx

I have a 2003 Discovery with 87k. I had one front driver's side die at 65k and the rear start to fade last week. So I have all 4 new ones. I think Denso makes the original O2's in your Rover. Bosch 02's come with a 1 year warranty. Recommended replacement every 100k from their website. You will also notice your gas mileage slightly increase!

 

My MPG was way more than a slight increase. I went from getting between 200-215 miles per tank to getting over 300 consistently. I didn't change the rears out yet. I actually just changed them out as they went bad.. The front drivers side went first so I order the 2 fronts and being the lazy fellow I am, just changed the on the had a problem... About 2 months later, I got the code for the passenger side front O2.

Still, after changing that one out though, didn't see any change in the MPG's from the first time.

Regards to all and good luck to the OP.