Silverado 2008

Heated Oxygen Sensor (HO2S)

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Location



Specific to:

Chevrolet Silverado 1500 2008

The Heated Oxygen Sensors (HO2S) are threaded into the exhaust pipes.

Operation



Specific to:

Chevrolet Silverado 1500 2008

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 is 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.

Component Description

Specific to:

Chevrolet Silverado 1500 2008

The Oxygen Sensor is a zirconium dioxide electronic device that measures the proportion of oxygen (O2) content in the exhaust gas. The sensor operates by measuring the difference between the oxygen content in the exhaust gas and the external air, and generates a variable voltage signal as the ratio between the two changes. The function of the oxygen sensor is to monitor the air-fuel ratio of the engine, determine if the mixture is rich or lean, and provide feedback (real-time information) to the Powertrain Control Module (PCM) so that the air-fuel ratio may be automatically adjusted.

Fuel Trim

Specific to:

Chevrolet Silverado 1500 2008

Fuel trim is the PCM parameter that is used to adjust the air-fuel mixture. The ideal HO2S feedback value is 0.45 volts DC, which is indicated when air and fuel are at the stoichiometric ratio of 14.7:1. This value is determined by oxygen sensor feedback, and provides the final data for the PCM in determining the correct air-fuel mixture.

Oxygen Sensor Heater

Specific to:

Chevrolet Silverado 1500 2008

In order to achieve operating temperature and enter closed loop more quickly, modern oxygen sensors have built-in heating elements.

Removal & Installation



4.3L Engines

Specific to:

Chevrolet Silverado 1500 2008


NOTE
Replace the sensor if the pigtail wiring, connector, or terminal is damaged. The external clean air reference is obtained by way of the sensor signal and heater wires. Any attempt to repair the wires or connectors could result in obstruction of the air reference. Make sure the lead wires are not sharply bent or kinked as the air reference could become blocked.

  1. Before servicing the vehicle, refer to the Precautions Section.
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Raise and support the vehicle safely.
  6.  
  7. Disconnect the CPA retainer.
  8.  
  9. Unplug the sensor connector. Remove the clip from the engine harness.
  10.  
  11. Remove the sensor from the exhaust pipe.

    Click image to see an enlarged view

    Fig. Oxygen sensor locations-4.3L engines

  12.  

To install:


NOTE
Be sure to use new fasteners, as required.

  1. Position the sensor on its mounting.
  2.  
  3. If reusing the old sensor, coat the threads with GM anti-seize compound 12377953 or equivalent.
  4.  
  5. New sensors are already coated; additional compound is not needed.
  6.  
  7. Tighten the sensor to 31 ft. lbs. (42 Nm).
  8.  
  9. Continue the installation in the reverse order of the removal procedure.
  10.  

4.8L, 5.3L & 6.0L Engines

Specific to:

Chevrolet Silverado 1500 2008


NOTE
Replace the sensor if the pigtail wiring, connector, or terminal is damaged. The external clean air reference is obtained by way of the sensor signal and heater wires. Any attempt to repair the wires or connectors could result in obstruction of the air reference. Make sure the lead wires are not sharply bent or kinked as the air reference could become blocked.

  1. Before servicing the vehicle, refer to the Precautions Section.
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Raise and support the vehicle safely.
  6.  
  7. On bank one, sensor one for the 2500 cab/chassis, 2500 and 1500 equipped with 4WD unbolt the front driveshaft from the front differential.
  8.  
  9. On bank two, sensor one for the 1500 and 2500 remove the right side wheelhouse liner.

    Click image to see an enlarged view

    Fig. Front wheelhouse liner and related components (right)

  10.  
  11. Disconnect the CPA retainer.
  12.  
  13. Unplug the sensor connector. Remove the clip from the engine harness.
  14.  
  15. Remove the sensor from the exhaust pipe.

    Click image to see an enlarged view

    Fig. Oxygen sensor locations (2500 cab/chassis)-4.8L, 5.3L & 6.0L engines



    Click image to see an enlarged view

    Fig. Oxygen sensor locations (1500 and 2500)-4.8L, 5.3L & 6.0L engines

  16.  

To install:


NOTE
Be sure to use new fasteners, as required.

  1. Position the sensor on its mounting.
  2.  
  3. If reusing the old sensor, coat the threads with GM anti-seize compound 12377953 or equivalent.
  4.  
  5. New sensors are already coated; additional compound is not needed.
  6.  
  7. Tighten the sensor to 31 ft. lbs. (42 Nm).
  8.  
  9. Continue the installation in the reverse order of the removal procedure.
  10.  

Testing



Specific to:

Chevrolet Silverado 1500 2008


NOTE
Refer to the Electrical Wiring Diagram for component and connector locations, connector views, and circuit-specific information.

Connection And Wiring Diagnosis

Specific to:

Chevrolet Silverado 1500 2008

Refer to the Electrical Wiring Diagram for component and connector locations, connector views, and circuit-specific information.

Many intermittent open or short circuits may be caused by wiring harness and connector movement due to vibration, engine torque, bumps and rough pavement, etc.

  1. Test the wiring harness and connectors by performing the following tests:

    Move the related connectors and wiring while monitoring the appropriate scan tool data.
     
    Move the related connectors and wiring with the component commanded ON and OFF. Using a suitable the scan tool, observe the component operation.
     
    With the engine running, move the related connectors and wiring while monitoring component operation.
     
    If harness or connector movement affects the data displayed, the component and system operation, or the engine operation, inspect and repair the harness or connections as necessary.
     

  2.  
  3. Test the connector terminal pins and/or wiring by performing the following tests:

    Inspect for incorrect mating of the connector halves, or terminals not fully seated in the connector body.
     
    Inspect for improperly formed or damaged terminals and test for incorrect terminal tension.
     
    Inspect for poor terminal to wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body.
     
    Inspect for corrosion or water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation with little visible evidence. Look for swollen and/or brittle sections of wire in the suspect circuits.
     
    Inspect for wires that are broken inside the insulation by gently pulling on suspect sections of wiring.
     

  4.  

Related Diagnostic Trouble Codes (DTC)

Specific to:

Chevrolet Silverado 1500 2008



Click image to see an enlarged view

Fig. Related Diagnostic Trouble Codes

Oxygen Sensor Heater

Specific to:

Chevrolet Silverado 1500 2008

The oxygen sensor heater may be tested by performing a resistance test; the sensor must be disconnected from the main engine wiring harness. If the circuit resistance is greater than 5.0 ohms, replace the HO2S. Refer to the Electrical Wiring Diagram for specific circuit information and connector views.

Click image to see an enlarged view

Fig. Normal pre-catalyst HO2S reading.



Click image to see an enlarged view

Fig. Normal post-catalyst HO2S reading.

Post-Catalyst HO2S (Sensor 2)

Specific to:

Chevrolet Silverado 1500 2008

A properly operating #2, or rear heated oxygen sensor (HO2S) should display flat feedback voltage of less than 0.2 volts DC. Use a suitable scan tool or a Graphing Multi-Meter (GMM) in order to view HO2S data.

If the feedback signal displays a cross-count, this is usually an indication of a faulty catalytic converter. If the feedback signal is flat, but is greater than 0.5 volts DC, additional diagnosis is required in order to determine the proper function of the HO2S, or if a fault exists in any related sub-systems.

Heated Oxygen Sensor Strategy

Specific to:

Chevrolet Silverado 1500 2008

The oxygen sensor operates most effectively when an operating temperature of 1,472° F (800° C) or higher is reached and maintained. When the oxygen sensor reaches the specified temperature and begins sending the feedback signal, the PCM uses the information to enter closed loop mode, which is defined as the PCM having full control of the air-fuel ratio. In order to achieve operating temperature and enter closed loop more quickly, modern oxygen sensors have built-in heating elements.

Pre-Catalyst HO2S (Sensor 1)

Specific to:

Chevrolet Silverado 1500 2008

A properly operating #1, or front heated oxygen sensor (HO2S) should display a cross count of eight oscillations or more within ten seconds, within a voltage range of 0.2 - 0.8 volts DC. Use a suitable scan tool or a Graphing Multi-Meter (GMM) in order to view HO2S data.

If the feedback signal is not within the specified range, additional diagnosis is required in order to determine the proper function of the HO2S, or if a fault exists in any related sub-systems.

 
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