I’m trying to diagnose a p0125 code on my 99 corolla. Toyota forums seem to say Toyota didn’t follow standards on this code and it is likely also the O2 sensor, can anyone confirm if this is the case?

I’m getting no other codes, and it will run for about 30 minutes before triggering again. Last time it triggered I saw exhaust smoke on the way home, which went away as soon as I reset the code. after clearing the code the exhaust while clear does seem to be rich smelling. Engine seems to run fine, I’m not noticing any performance issues, not signs of dipping oil/coolant amounts. coolant gauge is operating and hitting the halfway point normally.

I can’t think of anything else but the O2 sensor but I expected rougher performance and don’t really want to spend $125 on a part if I don’t have to.