[Lepak91]

The upper o2 sensor on the back side of the engine (near firewall) needs to be replaced. Any idea what the easiest way is to get it replaced? Do I have to take off the exhaust manifold to get to it? This would be a PITA since I have an ATX. I don't think I can get to it from the top.

 

[Fett]

You should be able to get to it from under the car, using an open face wrench.

If not, then drop the subframe.