Just wondering if I can access the driver side o2 sensor from the top through engine bay. I can't remember how I changed my first Disco 2's sensors, its been a while. I tried getting it from the bottom this time around with a offset wrench but I can't seem to get enough leverage on it. Also the thing won't budge. I already pb blasted it. Any suggestions would be much appreciated.

 

There was one time I used I think a crows foot wrench to break it.. wasn't on a Disco but may be worth a try

 

Pb blaster has been confirmed to not actually do jack. Try aix of ATF/Seafoam 50/50.

I always got at mine from underneath with a 12" box wrench. If that's still not enough you might have to get some extentions and some wobble joints to reach from up top with a breaker bar or torque wrench.

 

I did both my upstreams just a couple of weeks ago. It was tight getting to them, but not horribly so (the downstreams are worse). I can't imagine trying to get to either of them from above.
Spend the couple of dollars to get an offset O2 socket. It will make things much, much easier.

 

I went from underneath and used the offset tool from an O2 sensor tool kit. Easy.

 

Open end wrench has always got em off for me from underneath. I do spray em & let em soak for a bit first or crank it for a minute to warm up the pipes.

 

Pretty sure that was the one I did from the top.
They're all super awkward to get at. I found what works best is to get a well trained but extremely strong spider monkey with small hands to get them in and out.