Thank you for asking your question on Just Answer.
Enclose is location of the HO2S sensors.
3.8L Shown, 3.0L SimilarAll Heated Oxygen Sensors (HO2S) are located in the dual converter Y pipe: one at the inlet and outlet of each catalyst converter
The front 2 are HO2S sensors and the rear 2 are called cat monitors.
I see the diagram. This is great. But how do I get access to the HO2S on the back half of the engine? I don't have a lift.