bank one system too lean

A thorough inspection for vacuum or air intake leaks must be performed. A leaking or incorrect PCV valve is possible. Since you did not mention any other DTC's, it most likely is isolated to bank one. The most common part installed for this concern is an oxygen sensor, but often it is incorrect. A scan tool is needed that can monitor the fuel trims to accurately diagnose your concern.

As Brian said! Most likely a vacuum leak on the #1 bank or a bad fuel injector, but using a professional grade scan tool and analyzing scan tool data is what is needed to properly figure out what is wrong.