Circuit Description

PCM provides about .45 volt reference to Heated Oxygen Sensor (HO2S). HO2S sensor signal voltage varies from about one volt when exhaust is rich to about .1 volt when exhaust is lean. PCM constantly monitors HO2S signal during Closed Loop operation, and compensates for rich or lean condition by adjusting injector pulse width. If HO2S voltage remains at or near the .45 volt reference voltage for an extended period of time, DTC will set.

Conditions required to set DTC are:

• No related DTCs set.
• Engine has been running for at least 2 minutes.
• HO2S heater has been determined to be functioning properly (HO2S has warmed to operating temperature).
• HO2S signal voltage remains between .4-.5 volts for a total of 76.5 seconds over a 90-second period.