I need to replace my "middle" sensor on my 2001 4X4...how difficult is it to do this? This is the sensor right after the cat......thanks !

 

B1S2 is not the middle sensor, but the last sensor, the Post Cat sensor.

To remove it just get yourself the appropriate wrench, disconnect the electrical connection, and remove it.

In the future, please do not post the same question in multiple areas.

 

I just changed B1S2 it took about 5 minutes