I pulled a P0138 code (bank 1 sensor 2 HV) on my 03 qc hemi, another post reference 4 o2 sensors; I've only found 2, one before the cat and one after the cat both on the passenger side of the vehicle after the Y-intersection. I bought the downstream one after the cat, did I get the correct one? Are there only 2 sensors? Where are the other 2 sensors located?

Scott

 

There should be one before the cat on each side...for each bank of cylinders. But if you only have 1 cat, there would be only 1 post cat oxygen sensor. Either way, it sounds like you purchased the correct sensor as "sensor 2" is always the one further back.