ok, so I'm looking to swap out my o2 sensors for tune up. went to pep boys, advanced, autozone, none of which could tell me how many or what kind of sensors i have. i have been looking on here and am just confused. from what i under stand i have 4, 2 pre-cat, 2 after? I also saw a few posts on here saying i should buy the more pricey oem sensors? does it make a difference? sorry for the post, cant get the truck into a garage until next weekend too check it out and i am just really confused!

by the way 1998 blazer 4 door, auto.


so many mods to do, so little time haha

 

The 98+ trucks will have three O2 sensors, B1S1 & B2S1 (upstream = before cat) as well as B1S3 (downstream = after cat). The only ones you should be worried about for a tune up is the upstream sensors (B1S1 & B2S1).

I would recommend you purchase AC Delco sensors only. I have personally tested many different manufacturers on GM products and none had the out of the box activity of the AC Delco sensor. NGK were a close 2nd. Standard & Denso were not horrible. By far the worst sensor I have tested was the Bosch sensor.

 

Check out RockAuto for a pretty decent price on the AC Delcos. I got them there last month for cheaper than any of the local parts stores were selling the Bocsh, Denso, etc.

 

So I'm guessing all three o2 sensors are the same, as in same part number?
Thanks again for your help guys, I really appreciate it!



ACDELCO Part # AFS105 {#19178918, 25312200}
SENSOR,HTD OXY(POSN 3) POST CONVERTER
SENSOR,HTD OXY(POSN 2) PRE CONVERTER

 

The AFS105 is the proper sensor for any one of the three locations. If you are looking to replace them, only replace the two upstream sensors (the ones in the y-pipe closest to the engine) as these are the only ones that have anything to do with powertrain management. The other one is an emissions monitoring sensor only and should only be replaced after a code pops up for it and proper diagnostic steps have found the sensor to be faulty.