I have a 03 Expedition, 2x4, 4.6l engine w/ 101K miles. It has had a problem with a rough not quite grinding noise when it gets warm. It sounds like it was coming from underneath the drivers seat. I thought it was most likely the exhaust or catalytic converter area. I thought it was a rattle, but Saturday the check engine light came on and it was idling real rough (almost cutting out) and surging. I immediately thought O2 sensor. That is where my knowledge and experience stops. Took it to Autozone, and the following codes came up: P2195, P2197 and P0171. All of these pointed to the O2 sensors. My questions are as follows:

P2192 says "Lack of O2 sensor - Bank 1, Sensor 1"
P2197 says "Lack of O2 sensor - Bank 2, Sensor 1"
In my lack of time I replaced the front "up stream" sensors on the right and left. I still have the surging and rough idle! Where is Bank 1 and Bank 2? I assumed that since they both said sensor 1 I assumed they were the ones before the catalytic converter. Am I correct with O2 sensor?

I was also assuming that the P0171 was related to the bad O2 sensors. I have read that O2 sensor is often misdiagnosed for P0171.

Any direction will be greatly appreciated!

Thanks!

Mike