CEL just came on not too long ago, P 0138. I've read it's the O2 sensor
I keep reading that it's the sensor after the cat? Should I replace it? Try cleaning it first? I also saw somewhere it could be a clogged cat, but if the cat was clogged, I'd feel it. Any help?

 

same issue, any advice you get please pass along

 

How many miles on truck? Original O2 sensor?

If first question is over 89,000 and second is yes,,,,,,I would replace...Both of them...desno....

 

Replace it. Denso or NTK.

 

Miles, beats me. 255k km on it. And I'm assuming original O2. And the second part of my question is answered. I was going to ask what brand after searching rock auto. Thanks for the help. Going to order a new sensor now. And fix the cat this weekend.
Oh, lastly... the one I got to change.. that's after the cat, downstream, right?

 

Downstream-after cat
Upstream-before cat