"The catalyst monitor sensors operate the same as the fuel control sensors. Although the HO2S 2 sensor's main function is catalyst monitoring, it also plays a limited role in fuel control. If the sensor out-put indicates a voltage either above or below the 450 millivolt bias voltage for an extended period of time, the PCM will make sight adjustment to fuel trim to ensure that fuel delivery is correct for catalyst monitoring"
Taken out of page 4-9 of Chilton's General Motors - Century/Lumina/Grand Prix/Intrigue 1997-00 repair manual. Part number 28380
