Conditions For Setting DTC
WARNING: This page is about a different car, the 2003 Pontiac Sunfire, 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, and 2003 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
The PCM detects that the difference between the HO2S 1 rich-to-lean average transition time and the lean-to-rich transition time is more than a calibrated value.