Downstream Oxygen Sensors ( 1/2 and 2/2 )

Downstream Heated Oxygen Sensor 1/2 & 2/2:

The downstream heated oxygen sensors thread into the outlet pipe at the rear of the catalytic convertors.
The right side is 1/2 and the left side or driver's side is 2/2, the reason these are numbered this way is because the right bank of this V6 is where cylinder number 1 is located.