OK.......I crawled up under my truck today (05 Hemi Sport) to have a look at the O2 sensors.I only see 1 pre and 1 post cat.Am I not seeing the other 2 somewhere and if so where?I thought they had 2 on bank 1 and 2 on bank 2.I was especially stumped by the post cat. sensor since I was expecting to see an obvious location for them both.I have SIDO exhaust so my thinking was the post sensors would HAVE to be before the pipe splits right?



Never mind.........I looked again and found 'em both! My bad

 

Yep... 2 cats, one on each side, a sensor before and after each one...

 

When should we be checking these sensors and what benefit is there to changing them out?

 

I personally think they should be in your 100k tune up.
Not only do they pass you and stop from passing some inspections they control your Air/Fuel ratio, If the ratio isnt right count a few thousand miles off your motor if they go unfixed, they could leave you stranded if they all the sudden go out, and if you put the OEM NTK,NGK sensors back in you will maxamize the fuel you use.!!