I looked and I looked - and did a thorough search of my exhaust system. I've only found two oxygen sensors - one on the inlet of the catalytic convertor, one aft of the catalytic convertor.

So, where's the third one? My truck was built in August of '97, so would it only have two? If it does have 3, where would O2 sensor #3 be located?

 

if it is fed emisions you'll only have two. One before the cat and one after. If it's cali emissions then you'll have three cats and for o2 sensors. there is one cat right after each header and one cat after the y-pipe. there will be an o2 sensor before and after each of the cats right after the header. the third cat won't have anythimg. It sounds like you have fed emissions so you only have two o2 sensors.

 

Good to know! Ok, I guess I only have 2 then. That explains everything.