The code is P1131. This is on a 97 4.6 auto. The truck is running fine. It doesn't misfire run rough or anything of that sort. I have read a few other posts with the same code and I am going to check the vacuum lines. I'll report back with what I find if anything.

 

Upstream bank 1 O2 sensor is tired and worn out.

Suggest replacing both banks at the same time.

Steve