Oxygen Sensor Mod Issue / P0420

Yes, each time I changed something - sensor, mod, etc, I cleared the codes and started over.

 

Everything I've read on this topic points in this direction: S2 (for my rig) is just to monitor cat efficiency, and does not impact fuel trim.

 

There's one or two tech chat forums that state otherwise but they are wrong on many other topics.
2001 California emissions models and up. S1 is air/fuel
S2 is Oxygen

 

Mine is a 1st gen.

 

I am having the same issue, just wondering if anyone had that fixed !!!

 

Old thread, I know… I looked at the scan data again and I saw something that I did not see before, your coolant temp should be more stable. I dont know what temp it has to be to go into closed loop.