Conditions For Setting DTC
WARNING: This page is about a different car, the 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
The AF ECM monitors an O2S signal voltage stuck between 0.347 volt and 0.550 volt (inactive) for 9 seconds continuously or the AF ECM monitors an O2S signal voltage between 0.00 volts and 1.0 volt that has not performed a Rich/Lean switch for 15 seconds continuously.