Vibe 2006-2007

Heated Oxygen Sensor

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Operation



The Heated Oxygen Sensor (HO2S) is a device which produces an electrical voltage when exposed to the oxygen present in the exhaust gases. The oxygen sensors are electrically heated internally for faster switching when the engine is started cold. The oxygen sensor produces a voltage within 0 and 1 volt. When there is a large amount of oxygen present (lean mixture), the sensor produces a low voltage (less than 0.4v). When there is a lesser amount present (rich mixture) it produces a higher voltage (0.6-1.0v). The stoichiometric or correct fuel to air ratio will read between 0.4 and 0.6v. By monitoring the oxygen content and converting it to electrical voltage, the sensor acts as a rich-lean switch. The voltage is transmitted to the PCM.

Two sensors per bank are used, one before the catalyst and one after. This is done for a catalyst efficiency monitor that is a part of the diagnostic system of the engine controls. The one before the catalyst measures the exhaust emissions right out of the engine, and sends the signal to the PCM about the state of the mixture as previously talked about. The second sensor reports the difference in the emissions after the exhaust gases have gone through the catalyst. This sensor reports to the PCM the amount of emissions reduction the catalyst is performing.

The oxygen sensor will not work until a predetermined temperature is reached, until this time the PCM is running in what as known as open loop operation. Open loop means that the PCM has not yet begun to correct the air-to-fuel ratio by reading the oxygen sensor. After the engine comes to operating temperature, the PCM will monitor the oxygen sensor and correct the air/fuel ratio from the sensor's readings. This is what is known as closed loop operation.

Removal & Installation



Front Sensor
  1. Remove the engine cover.
  2.  
  3. Note the routing of the Heated Oxygen Sensor (HO2S) electrical harness.
  4.  
  5. Disconnect the HO2S electrical connector.
  6.  
  7. Using a suitable Oxygen sensor socket remove the sensor.
  8.  

To install:


NOTE
A special anti-seize compound is used on the HO2S threads. The compound consists of a liquid graphite and glass beads. The graphite will burn away but the glass beads will remain, making the sensor easier to remove. New or service sensors already have the compound applied to the threads. If the sensor is removed and is to be reinstalled, the threads must be coated with an anti-seize compound before reinstallation.

  1. If reinstalling the old HO2S, coat the threads with anti-seize compound.
  2.  
  3. Carefully install the HO2S to the pipe. Tighten the sensor to 32 ft. lbs. (44 Nm).
  4.  
  5. Attach the sensor electrical connections.
  6.  

Rear Sensor
  1. Remove the carpet retaining pin from the front floor console.
  2.  
  3. Pull back the carpet from the area near the front floor console. .
  4.  
  5. Note the routing of the Heated Oxygen Sensor (HO2S) electrical harness.
  6.  
  7. Disconnect the HO2S electrical connector.
  8.  
  9. Using a suitable Oxygen sensor socket remove the sensor from below the vehicle.
  10.  

To install:


NOTE
A special anti-seize compound is used on the HO2S threads. The compound consists of a liquid graphite and glass beads. The graphite will burn away but the glass beads will remain, making the sensor easier to remove. New or service sensors already have the compound applied to the threads. If the sensor is removed and is to be reinstalled, the threads must be coated with an anti-seize compound before reinstallation.

  1. If reinstalling the old HO2S, coat the threads with anti-seize compound.
  2.  
  3. Carefully install the HO2S to the pipe. Tighten the sensor to 32 ft. lbs. (44 Nm).
  4.  
  5. Attach the sensor electrical connections.
  6.  

Testing



  1. Turn OFF the ignition.
  2.  
  3. Disconnect the HO2S connector.
  4.  
  5. Measure the resistance of the HO2S, between the heater control and the ignition voltage circuits. If the resistance is not 1.8-3.4 ohms at 20°C (68°F), replace the sensor.
  6.  
  7. Turn ON the ignition, with the engine OFF.
  8.  
  9. Probe the ignition voltage circuit of the HO2S with a test lamp connected to a good ground. If the lamp does not illuminate, check the wiring circuit, for an open, short or high resistance.
  10.  
  11. Connect the HO2S.
  12.  
  13. Using a test lamp connected to a good ground, backprobe the HO2S heater control circuit at the powertrain control module (PCM) connector.
  14.  
  15. Turn ON the ignition, with the engine OFF. If the test lamp does not illuminate, check the heater control circuit of the HO2S for an open or a high resistance.
  16.  
  17. If there are no issues with the wiring and connectors, replace the sensor.

    Click image to see an enlarged view

    Fig. Heated Oxygen Sensor (HO2S) 1 sensor terminals; (1) HO2S1 Input, (2) HO2S1 Heater Feed Circuit, (3) HO2S1 Heater Control, (4) Low Reference



    Click image to see an enlarged view

    Fig. Heated Oxygen Sensor (HO2S) 2 sensor terminals; (1) HO2S2 Feed Circuit, (2) HO2S2 Heater Control, (3) Ground, (4) HO2S2 Heater Control

  18.  

 
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