It's me again. Have a 2011 ford taurus sho. I've replaced plugs and wires, couple ignition coils and all injectors. A little over a week ago I was getting a P0128 code. I replaced the thermostat this summer (was overheating but it needed new cooling fan). I relearned the values, I went to have it scanned today and I did nothing over a week ago and the code did NOT reappear. Was it a fluke? When I brought it back to Oreillys today the only codes that showed up were p0420 and p0430. My mechanic did a back pressure test on the cats 6 months ago and said they weren't bad. I have little mechanical aptitude but it seems to be pointing me to bad 02 sensors?