Note. For circuit reference, see WIRING DIAGRAMS article.
Circuit Description
PCM continuously monitors Heated Oxygen Sensor (HO2S) No. 1 activity. During monitoring period, PCM counts number of time that rich to lean and lean to rich responses are indicated. PCM then combines these counts with amount of time it took to complete transitions. With this information, an average time for each transition can be determined. If average response time is too slow, DTC will set. A lean to rich transition is indicated when HO2S No. 1 voltage changes from less than 300 millivolts to greater than 600 millivolts. A rich to lean transition is indicated when HO2S No. 1 voltage changes from greater than 600 millivolts to less than 300 millivolts.