Envoy, Rainer, Trailblazer 2006-2007

Heated Oxygen Sensor

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Operation



Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by the ignition 1 voltage circuit through a fuse. With the engine running, ground is provided to the heater by the HO2S heater low control circuit, through a low side driver within the Engine Control Module (ECM).

The ECM commands the heater ON or OFF to maintain a specific HO2S operating temperature range. The ECM monitors the voltage on the HO2S heater low control circuit for heater fault diagnosis. If the ECM detects that the HO2S heater low control circuit voltage is not within a specified range.

Removal & Installation



  1. Disconnect the negative battery cable.
  2.  
  3. Raise and safely support the vehicle, if necessary.
  4.  
  5. Disconnect the Heated Oxygen Sensor (HO2S) electrical connector.
  6.  
  7. Remove the HO2S using a J-39194-B.

    Click image to see an enlarged view

    Fig. Heated Oxygen Sensor (HO2S) 1 and electrical connector-4.2L engine shown

  8.  

To install:

  1. Coat the threads of the heated oxygen sensor with the anti-seize compound P/N 5613695, or the equivalent if necessary.
  2.  
  3. Install the heated oxygen sensor using a J-39194-B and tighten to 30 ft. lbs. (41 Nm).
  4.  
  5. Connect the HO2S electrical connector.
  6.  
  7. Lower the vehicle, if raised.
  8.  
  9. Connect the negative battery cable.
  10.  

Testing



  1. Disconnect the affected Heated Oxygen Sensor (HO2S).
  2.  
  3. Turn ON the ignition, with the engine OFF.
  4.  
  5. Probe the ignition 1 voltage circuit of the HO2S harness connector on the engine harness side with a test lamp that is connected to a good ground, and if the lamp does not illuminate, repair the open or high resistance in the circuit.
  6.  
  7. Turn OFF the ignition.
  8.  
  9. Probe the HO2S heater low control circuit of the HO2S harness connector on the engine harness side with a test lamp connected to battery voltage and observe the test lamp with the ignition still OFF.
  10.  
  11. If the test lamp illuminates, test the HO2S heater low control circuit for a short-to-ground and if it does not illuminate, start the engine with the test lamp still connected and check if the test lamp is ON steady or blinking.
  12.  
  13. Test the ignition 1 voltage circuit on the sensor side of the HO2S connector for a short-to-ground and if the sensor is shorted to ground, then replace the affected HO2S. If there is no short-to-ground, check for an intermittent condition.
  14.  
  15. Start the engine with the test lamp still connected and if the test lamp is ON steady or blinking, measure the resistance of the HO2S heater low control circuit and the ignition 1 voltage circuit with a Digital Multi-Meter (DMM), then check the HO2S heater low control circuit for a short-to-voltage.
  16.  
  17. Test the HO2S heater low control circuit for a short-to-ground, and repair if necessary. If there is no short-to-ground, test for shorted terminals and poor connections at the Engine Control Module (ECM).
  18.  
  19. Test the HO2S heater low control circuit for a short-to-voltage and repair, if necessary. If there is no short-to-voltage, test the circuit for an open or high resistance.
  20.  
  21. Test the HO2S heater low control circuit for an open or high resistance and repair, if necessary. If there is no open or high resistance in the circuit, test for shorted terminals and poor connections at the ECM.
  22.  
  23. Measure the resistance of the HO2S heater low control circuit and the ignition 1 voltage circuit with a Digital Multi-Meter (DMM), and if the resistance of either circuit is more than 3 ohms then repair the open or high resistance in the circuit, and if it is less than 3 ohms, test for shorted terminals and for poor connections at the HO2S.
  24.  
  25. Test for shorted terminals and poor connections at the HO2S and repair, if necessary. If there are no shorted terminals or poor connections, replace the affected HO2S.
  26.  
  27. Inspect the fuse and replace, if necessary.
  28.  
  29. Clear the DTCs with a scan tool.
  30.  
  31. Turn OFF the ignition for 30 seconds.
  32.  
  33. Start the engine.
  34.  
  35. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
  36.  
  37. Observe the Capture Info with a scan tool.
  38.  
  39. Check for any un-diagnosed DTCs.
  40.  

 
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