DTC P0140: Heated Oxygen Sensor No. 2 Circuit Insufficient Activity ("A" & "B" Series): Description

The PCM supplies a bias voltage of about 450 millivolts between the Heated Oxygen Sensor (HO2S) high signal circuit and HO2S low signal circuit. When measured with a 10-megohm DVOM, this may display as low as 350 millivolts. The oxygen sensor signal varies from about 800 millivolts when exhaust is rich, to about 50 millivolts when exhaust is lean

PCM constantly monitors the HO2S signal during closed-loop operation, then compensates for a rich or lean condition by decreasing or increasing the injector pulse width as necessary. If HO2S 2 voltage remains at or about the 450 millivolts bias for an extended period of time, DTC will set.