Oxygen Sensor Replacement on 4.8is
 

Hi guys,

My 4.8is X5 (E53) has 112K miles, I think the O2 sensors are original. My gas mileage is okay, I suppose. I was thinking of replacing the pre-cat O2 sensors prematurely, but I saw on the DIY for the 3.0 model (m54) you need to re-route the cables back to the engine. Is it different on the N62 4.8is? Do I need to route back to the engine? It looks like from under the truck it connects to a box mounted right on the transmission. If that is the case, it looks pretty easy (which is relative I suppose).

Thoughts?

Dude, the bentley manual sux for our cars, and not many specific DIYs out there for us. I had to do my Tstat, looked at DIYs here and was expecting lots of headache. Did the job in 15 min. 5 min was taking the plastic under ride cover off. 1 min to pull the fan out, two clips, two harness connections. That's it. Thermostat was 3 bolts and a hose. What I have noticed is that the 4.8is is made like a race car. Working on it is just too easy. Could really be as easy as you think for the o2. Give it a shot, let us know. I just haven't gotten the need to replace mine yet. I get 11.7 mpg. NYC and heavy foot, the power and noise is irresistible.

Why replace them if they are working fine? Any codes?

No codes, but it's generally recommended to replace them at 100k. I suppose they degrade over time, causing poor mileage.

They look to be in the same place as the 4.6, and if thats the case then it took me 5 minutes per side to do mine. The connections are clipped to the body and gearbox, and are easy to reach especially if you can get the car up in the air. Disconnect the wiring and slide a ring spanner down the wiring to the sensor, dont use an open ender as you might damage the flats.