My '01 Ram 5.2L threw a code P0138, it looks to be the O2 Sensor after the cat. I crawled under there today, rain and all, to see how easy or difficult it would be. Getting the old one out looks pretty easy. I tried following the wire to see where it was plugged in, but it appeared to be somewhere up on top of the tranny housing. Does that sound right? If so , I may have to do the plug in by feel. I'm going to give it a shot tomorrow if it ever stops raining.

 

The plug is usually on top of the tranny.

 

Yes, the plug is on top of the Tranny. I just replaced mine and it was fairly easy. just make sure to be patient with the clip. It is a two part, I broke the first part but the second part has kept it together just fine. Also just pull the wire a little and it should give you some more room.

 

Looks like the plug part is definitely going to be by feel, up there on the tranny