My 02 sensors have gone out and require replacement. However even with the aid of the internet, people, and even this website, I cant get a definitive answer on which 02 sensors I need. I have three common answers. All ac delcos of course, afs123, afs75, and afs97. Its a 96 trans am. So are all four sensors the same? Are pre and post cat sensors different? I am at a total loss here. Everyone is telling me something different, and that what the last guy said is wrong. A google search has not helped me yet. So I'm asking the experts. You guys.

 

Pre-cat and post-cat are different and have different connectors (rectangle vs square).

AFS75 is the p/n for AC Delco pre-cat sensor. People say they "changed" the design in the past few years because they look different from the factory ones. Factory is up top, new AFS75 is bottom.



But it really sounds like BS because here's what the Denso 2344012 sensor looks like. It's 2/3 the price.



You probably get Densos in an AC Delco box.

 

You don't say which ones you need, so I am sure that causes some confusion in itself. Front and rear O2s are not the same part number.

 

If you are going by trouble codes:

Bank 1 sensor 1= side of engine for cylinder #1 and sensor before the cat
Bank 1 sensor 2= side of engine for cylinder #1 and sensor after the cat
Bank 2 sensor 1= side of engine for cylinder #2 and sensor before the cat
Bank 2 sensor 2= side of engine for cylinder #2 and sensor after the cat