2000 Tj, 4.0, new crate engine pulled a PO138 code, Oxygen Sensor, Bank One, Sensor two. On mine I have a split exhaust on the 4.0, one sensor on the "Front" pipe and one on the back. I understand those sensors are the same, so I'm trying to determine which one is the one that needs to be replaced - Bank one, Sensor two. "Front" one or the back one?
Also, at the parts store they list two sensors "Upstream" from the cat, and one behind, they show a sensor on the cat itself right before the muffler, there is no sensor on mine, on the cat itself, and I don't see any wire connector down there that would go to it. I've owned the truck for ten years from 32,000 miles and it's never been replaced.
I also pulled a PO445, large vacum leak, I can't find anything, but I don't have a stock gas cap, so I'm going to start there
Any insight would be greatly appreciated, I don't want to spend the money and replace the wrong sensor.