Conditions For Setting DTC

WARNING: This page is about a different car, the 2002 Pontiac Firebird and 2002 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.

The post-HO2S voltage remains within 150 mV of the bias voltage, about 450 mV.
The amount of time depends on engine coolant temperature at start-up, and on the average air flow since start-up.