P0139 (M) 1/2 O2 Sensor Slow Response Oxygen sensor response not as expected

Ok, so what does this mean? I saw something about it being the downstream O2 sensor. I also read something about platinum plugs may be the cause....is this true?

 

The O2 has a heating element on it. So it can start sooner at operating temperature. If that heating element is acting up, that can cause a slow response. So it may be the 02 dieing, or it was 1 time of acting up. It best to reset the codes then see if it comes back again.

 

I have been pulling a car trailer loaded for about 500 of the last 750 miles and I seriously don't think that this truck had done that much towing for most of its life.

I wonder if the extra load was enough to cause this. I never pulled it over 60 with the O/D locked out. It was running about 1925-2000 rpms at speed.

Incidentally, I lost about 2 miles to the gallon about a month ago (before I started pulling that trailer up and down the road).

Come to think of it...it popped up this morning and last night was a pretty cold night and it has definitely gotten colder today.