Don't let the salesmen at Autozone diagnose your problems, let them stick to reading the codes. It is possible that a P0174 might be a bad O2 sensor. However, when I got the P0174 code it was due to my lower intake manifold o-rings leaking air. If that is what the problem is, Ford will repair it for free under Owner Notification Program 00M12. The price on the O2 sensor is a good price, however if that isn't your problem then you just wasted your money regardless of how good the price is.
You need further diagnosis to determine the reason your engine is reading lean on bank 2. The troubleshooting steps to diagnose a leaking lower intake manifold o-ring is to spray propane around the lower intake manifold while monitoring your short-term fuel trims. Watch for sudden changes when the propane is being sprayed or taken away. I the fuel trims make sudden jumps, then you have air leaking through your o-rings. A new O2 sensor will not fix that. With an OBD-II scanner you can also perform O2 sensor diagnostics. Compare the response of all four of your sensors. If they all behave the same way, then they are probably fine. If one is very slow to respond or doesn't respond at all then it is bad. The code will only tell you what the engine is seeing, not what is causing it.
