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/fuel ratio) in the exhaust produces a voltage signal less than 0.4 volt. A low concentration of oxygen (rich air/fuel ratio) produces a voltage signal greater than 0.6 volt. The HO2S provides feedback to the PCM indicating air/fuel ratio in order to achieve a near stoichiometric air/fuel ratio of 14.7:1during closed loop engine operation. The HO2S generates a voltage between 0.0 and 1.1 volts.
Embedded with the sensing element is the HO2S heater. The heating element heats the sensor to a temperature of 800°C (1,472°F). At approximately 300°C (572°F) the engine can enter closed loop operation. 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.
Removal & Installation
2.7L, 3.5L & 5.7L Engines
- Raise and support vehicle.
Disconnect wire connector from HO2S sensor.
NOTEWhen disconnecting sensor electrical connector, do not pull directly on wire going into sensor.
- Remove the HO2S sensor with an oxygen sensor removal and installation tool.
- Clean threads in exhaust pipe using appropriate tap.
- Install the HO2S sensor and tighten to 30 ft. lbs. (41 Nm).
- Connect the HO2S sensor wire connector.
- Lower the vehicle.
2.7L, 3.5L & 5.7L Engines
This procedure checks the heater circuit of the HO2S.
- Warm up the engine until operating temperature is reached.
- Turn the ignition off.
- Wait a minimum of 8 minutes to allow the O2 Sensor to cool down before continuing the test. Allow the O2 Sensor voltage to stabilize between 4.6-5.0 volts.
- With the ignition on, engine not running.
- Install a scan tool, actuate the HO2S heater test.
- With the scan tool, monitor O2 Sensor voltage for at least 2 minutes.
- If the voltage stays above 4.5 volts, turn the ignition off. (If not problem maybe intermittent).
- Allow the O2 sensor to cool down to room temperature.
- Disconnect the HO2S sensor harness connector.
- Measure the resistance of the O2 heater element, between the HO2S heater control terminal and the O2 heater ground terminal in the HO2S sensor connector.
- HO2S heater element resistance values should be measured at 21.1°C (70°F). The resistance value will vary with different temperature values.
- The resistance of the HO2S sensor heater element should be between 2.0-30.0 ohms.
If the resistance is not as stated replace the HO2S sensor.