Oxygen sensor How to tell if it is bad

You only have to do the upstream one. The downstream is just a tattle tale for your cat efficiency. I've never heard of either of those meals but they sound like expensive Italian food, when I was growing up it was Velveeta and chicken nuggets haha

 

2005 Double Cab, 2WD, long bed, Pre-Runner 250,000 miles. Original owner.
Four new O2 Toyota sensors. (Replacing originals)
MPG went from 19 to 23mpg.
Never has it run smoother. Found wrong p/n sensor left bank upstream. Was the same p/n as the Right bank upstream. Physically different also.
I had a CEL with RH upstream triggering code and RH downstream sketchy. 250k miles is fair for a new set. Stoked with the smooth engine and mileage !

 

Nice. I’ve replaced 2 of mine I should have done all 4. Maybe soon, as I’m pushing 260k on mine.

 

We have had cold mornings and it’s never started and ran so smooth. Runs smooth everywhere. Not that it was rough. Just a bit of a rumble I thought a fresh set of plugs would fix. It didn’t. I’m stoked I only did the one thing and the results couldn’t have been better.
My thoughts with a factory set is that maybe Toyota have good quality assurance over their parts. Maybe a set of Denso sensors from Toyota are closer matched than from Amazon. I have no clue. If I had changed them at 125,000, I would have saved $6,000 + in gas.
Maybe I’ll change them at 350,000 and sell them as a good working set on Craigslist.