"Bank 1" is refered to the # 1 cyl. which on the v6 stang the # 1 cyl. is loc. on the passanger side.
-DTC 171 (Fuel System Too Lean)
Now what this means is that you are running too lean on the # 1 cyl. side (pasgr side). Your O2 sensor which is on the exhaust manifold is sensing too much air passing by. This could be a "vacum leak" somewhere in your exhaust manifold. Your stang is just sucking in extra unmeasured air, wich is one of the causes for the 171 DTC to be set. Check your exhaust manifold or headers, check the exhaust gaskets, the bolts, nuts & washers make sure they are tight, listen for leaks, use soapy water in a spray bottle. Remember that a hole in your exhaust the size of a "pin-hole" can cause a lean condition!
Hopefully this can help you, this is from expierence on my 01' v6 stang, same problems, same DTC's till i found out my exhaust manifold was cacked on the bottom, tiny little crack.