Need help with a DTC 037 CEL
 

Folks I need some advice on what to do with a CEL. The code is 037 and 037P. From my understanding it means the the #1 bank is low. I think this has something to do an oxygen sensor. My first question is which oxygen sensor (before the cat or after the cat)? 2nd question is what does it mean by low:Wconfused? Should I actually replace the sensor or is something etc.? Any help is appreciated. Thanks.

Nobody can shed anymore light on this for me?