Running lean can be caused by many things. I just had problems today with a Lexus and an Infinity running lean and the codes flagged ended up not being the real source of the problem. Lean conditions on both banks makes it unlikely to be a bad air-fuel ratio/Oxygen Sensor. It is more likely caused by a vacuum leak, an air flow meter or map sensor that is not supplying the correct information to the on board computer in your car, insufficient fuel pressure or delivery. Reading and interpreting scan tool information is important in fixing the problem. One key piece of information from scan tool data is Long and short term fuel trim figures for both banks of cylinders and map voltage /air flow measured in grammes at different engine RPM and load. Sorry no easy fix without being able to see scan tool readings and listening to the engine to hear if it has a misfire or vacuum leak.