Circuit Description

PCM monitors the Heated Oxygen Sensor (HO2S) activity for 100 seconds. During this period, PCM counts the number of times that the HO2S switches from rich to lean and lean to rich. When PCM determines that the HO2S did not switch enough times, DTC will set.

A lean to rich switch is determined when the HO2S voltages changes from less than 300 mV to greater than 600 mV. A rich to lean switch is determined when the HO2S voltage changes for greater than 600 mV to less than 300 mV.