Conditions For Setting DTC
WARNING: This page is about a different car, the 2003 GMC Sonoma and 2003 Chevrolet S10 Pickup. However, it is still accessible from the selected car via links, so may be relevant.
PCM detects that the O2S 1 rich-to-lean transitions is less than 2 or the lean-to-rich transitions is less than 2.