Conditions for Setting the DTC: P013D
WARNING: This page is about a different car, the 2009 GMC Sierra and 2009 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The ECM detects that the accumulated mass air flow monitored during lean-to-rich transitions between 350-650 mV is more than 50 grams.