Conditions for Setting the DTC
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 HO2S voltage is between 400-520 mV for more than 10 minutes.
OR
The ECM detects that the measured internal resistance of the HO2S is more than 40,000 ohms, when the calculated exhaust temperature is more than 600°C (1,112°F).