Heated Oxygen Sensors (HO2S) - Post-Catalyst (Rear)

The Heated Oxygen Sensor (HO2S) produces a voltage that varies between 100 mV and 900 mV under normal operating conditions. The Engine Control Module (ECM) produces a bias voltage on the HO2S signal circuit of 420 to 480 mV. The reference ground for the sensor is provided through the ECM. The ECM monitors the signal voltage to determine if the exhaust is lean or rich. The oxygen sensor voltage is high when the exhaust is rich, and low when the exhaust is lean. The ECM constantly monitors the HO2S signal during the closed loop operation.