It will be on the passenger side, before the Cat convertor.
Here is the location for all 4 sensors.
If you have further questions on this, please feel free to reply.
Have you owned the vehicle since it was new?
If so has that sensor ever been replaced before?
Does it look like the harness connector has been spliced?
There are alot of "universal" O2 sensors out there that have to be spliced...
Which size engine?
You dont have to pay for each reply :-)
I dont have a picture, but this is what GM shows for thr part number...
Thanks for asking!