I'm getting 2 codes a p1131 and a p0171 on my ford Taurus ses 3.0l. I'm thinking upstream o2 sensor any thoughts?

 

you might be killing the messenger instead of fixing the problem. A lean condition, which is indicated by both codes, is often caused by a vacuum leak. Low fuel pressure could also be a reason.
Look for vacuum leaks first, then check the fuel pressure, replace the fuel filter maybe.

But trust that HO2 sensor. It was sensing something.

 

So your saying it's not the 02 sensor? Where would I start looking for this leak? Since I'm not getting a evap emissions leak it's not there. Where is the fuel filter on this car, under the driver side back door? Could it be a PVC valve?

 

Yes, i am saying that the sensors did their job as designed. If you change them out the code will reappear after a short time and that will proof that the sensors you threw away were just fine.

Go to Youtube and type "finding vacuum leaks". There are many methods.