I recently had a tranny change on my 2000 with 70000 miles +. Coincidentally after getting it back from the dealer the check engine light came on . It turned out to be for the o2 sensor #2. The dealer wanted $133 so I obtained from it from hparts for $81. I was a bit intimidated at first to do the job myself but after talking to some of my diy friends it seemed something I could handle. And I did! Just be sure to jack up the front of the vehicle safely and have someone around when you are under the vehicle. All you need to do the job is a 22mm or 7/8 open end spanner. It was not difficult to remove. The old sensor had a dent in the casing where the wires enter.Was it done at the dealer during the tranny change? Or perhaps hit by road debris? I really cannot say!! Cheers!