Yup, the sensor is hard to get at, but not impossible. I found it easiest to lay a flattend out box on the UIM so I had a place to neel down on top of the engine. A flashlight, a 3/8" breaker bar, and an O2 socket did the trick. IIRC there is a fuse/link or big wire down in that area that likes to get in the way.
