Circuit Description

When Heated Oxygen Sensor 2 (HO2S 2) temperature reaches about 600°F (316°C), it becomes an electrical source that responds to the oxygen content in the exhaust. PCM produces a bias voltage of about 450 mV on the oxygen sensor circuit. When sensor is cold, its internal resistance is extremely high; therefore, the PCM recognizes the bias as an open circuit. As the sensor warms up, the internal resistance decreases. When sensor reaches about 600°F (316°C), it starts producing a voltage based on the oxygen content in the exhaust stream.

DTC P0140 will set if HO2S 2 voltage is 391-491 mV for 90 seconds when engine is at normal operating temperature, engine is running for more than one minute, and no other engine sensor or misfire DTCs have been set or commanded air/fuel ratio is about 14.7:1. HO2S 2 signal is continuously monitored once these conditions are met.