P0031, P0037, P0051, and P0057
WARNING: This page is about a different car, the 2009 Pontiac Torrent and 2009 Chevrolet Equinox. However, it is still accessible from the selected car via links, so may be relevant.
The ECM detects a ground in the heater circuits of the HO2S when the heater is commanded OFF. The condition exists for greater than 4 seconds or a cumulative of 30 seconds.