From my experience I replaced the o2 sensor upstream of the cat. Cleared the lean error. Afterwards the po133 error came up. I replaced the downstream(after cat sensor). No more error codes. It probably is best to replace both. They eventually foul up or breakdown. Not a guaranty but it worked for me.
Okay and what o2 sensor do I get?
From my experience I replaced the o2 sensor upstream of the cat. Cleared the lean error. Afterwards the po133 error came up. I replaced the downstream(after cat sensor). No more error codes. It probably is best to replace both. They eventually foul up or breakdown. Not a guaranty but it worked for me.
I got both for less than $60 online.