Conditions for Setting the DTC
WARNING: This page is about a different car, the 2004 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.
The PCM detects that the HO2S 1 voltage had fewer rich to lean switches than a calibrated value during a 90 second monitoring period.
Or
The PCM detects that the HO2S 1 voltage had fewer lean-to-rich switches than a calibrated value during a 90 second monitoring period.