Hi,
Can I exchange the front O2 sensor for the rear one?
Are they the same? (the one in front of the cat and the one there to just check if the cat is working)
I think my front one is shot and I want to see if it is before replacing it.
Thanks.

 

The connectors are different shape.

If you think one of the pre-cat sensors is "shot", swap the left and right pre-cat sensors, and see if the problem follows the sensor.