Condition 1

WARNING: This page is about a different car, the 2006 Buick LaCrosse and 2006 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.

The ECM detects that the front HO2S is operating too rich while the rear HO2S is operating too lean and the ECM detects that the fuel trim is at minimum control.
OR
The rear fuel trim, long and short term, is less than a threshold.
This DTC sets after the air flow coming into the engine accumulates to more than 200 grams and the above conditions are met for more than 4 seconds.