Heated Oxygen Sensor (Ho2S)
The HO2S detects the presence of oxygen in the exhaust and produces a variable voltage according to the amount of oxygen detected. A high concentration of oxygen (lean air to fuel ratio) in the exhaust produces a voltage signal less than 0.4 volt. A low concentration of oxygen (rich air to fuel ratio) produces a voltage signal greater than 0.6 volt. The HO2S provides feedback to the PCM indicating air to fuel ratio in order to achieve a near stoichiometric air to fuel ratio of 14.7 to 1 (9 to 1 E100) during closed loop engine operation.
When the oxygen sensor is cold, disconnected or on initial start up, the voltage may read between 1.5 to 1.7 volts. The oxygen sensor voltage will decrease to the normal operating range of 0.0 to 1.1 volts during warm, stabilized engine running conditions.
The HO2S heater is embedded with the sensing element. The heating element heats the sensor to a temperature of 800°C (1, 472°F). At approximately 300°C (572°F) the engine enters closed loop operation. The VPWR circuit supplies voltage to the heater. The PCM turns the heater ON by providing the ground when the correct conditions occur. The heater allows the engine to enter closed loop operation sooner. The use of this heater requires the HO2S heater control to be duty cycled, to prevent damage to the heater.