Subaru Forester 1998-05

Heated Oxygen Sensor

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Operation



The exhaust gas oxygen sensor supplies the electronic control assembly with a signal which indicates either a rich or lean mixture condition, during the engine operation.

Removal & Installation



2.5L DOHC Engine
Front Sensor
  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the connector. Disconnect the engine harness clip.
  4.  
  5. Raise and support the vehicle safely. Remove the tire and wheel.
  6.  
  7. Remove the service hole cover.
  8.  
  9. Remove the oxygen sensor.
  10.  

To install:

  1. Installation is the reverse of the removal procedure.
    NOTE
    Apply anti-seize compound to the threaded portion of the sensor, prior to installation. Never apply anti-seize compound to the protector of the sensor.

  2.  
  3. Tighten the sensor to 22.1 ft. lbs.
  4.  

Rear Sensor
  1. Disconnect the negative battery cable.
  2.  
  3. Raise and support the vehicle safely.
  4.  
  5. Disconnect the connector. Remove the clip by pulling it out from the upper side of the crossmember.
  6.  
  7. Remove the oxygen sensor.
  8.  

To install:

  1. Installation is the reverse of the removal procedure.
    NOTE
    Apply anti-seize compound to the threaded portion of the sensor, prior to installation. Never apply anti-seize compound to the protector of the sensor.

  2.  
  3. Tighten the sensor to 22.1 ft. lbs.
  4.  

2.5L SOHC Engine
  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the clip fastening the harness. Disconnect the connector.
  4.  
  5. Raise and support the vehicle safely.
  6.  
  7. Remove the engine under cover, as required.
  8.  
  9. Remove the oxygen sensor.
  10.  

To install:

  1. Installation is the reverse of the removal procedure.
    NOTE
    Apply anti-seize compound to the threaded portion of the sensor, prior to installation. Never apply anti-seize compound to the protector of the sensor.

  2.  
  3. Tighten the sensor to 15.2 ft. lbs.
  4.  

Testing



2.5L DOHC Engine
Front Sensor

Perform a visual inspection of the sensor as follows:

  1. If the sensor tip has a black/sooty deposit, this may indicate a rich fuel mixture.
  2.  
  3. If the sensor tip has a white, gritty deposit, this may indicate an internal coolant leak.
  4.  
  5. If the sensor tip has a brown deposit, this could indicate oil consumption.
  6.  
  7. Measure the resistance of the harness between the sensor connector terminals (terminals 1 and 2).
  8.  
  9. If measured value is more than 5 ohm, replace the sensor.

    Click image to see an enlarged view

    Fig. Front oxygen sensor connector location-Forester 2004-2006 2.5L DOHC engine

  10.  

Rear Sensor

Perform a visual inspection of the sensor as follows:

  1. If the sensor tip has a black/sooty deposit, this may indicate a rich fuel mixture.
  2.  
  3. If the sensor tip has a white, gritty deposit, this may indicate an internal coolant leak.
  4.  
  5. If the sensor tip has a brown deposit, this could indicate oil consumption.
  6.  
  7. Turn the ignition switch OFF.
  8.  
  9. Measure the resistance of the harness between the sensor connector terminals (terminals 1 and 2).
  10.  
  11. If measured value is more than 30ohm, replace the sensor.

    Click image to see an enlarged view

    Fig. Rear oxygen sensor connector location-Forester 2004-2006 2.5L DOHC engine

  12.  

2.5L SOHC Engine
Front Sensor

Perform a visual inspection of the sensor as follows:

  1. If the sensor tip has a black/sooty deposit, this may indicate a rich fuel mixture.
  2.  
  3. If the sensor tip has a white, gritty deposit, this may indicate an internal coolant leak.
  4.  
  5. If the sensor tip has a brown deposit, this could indicate oil consumption.
  6.  
  7. Check the exhaust system for defects.
  8.  
  9. Replace the sensor, as required.
  10.  

Perform a visual inspection of the sensor as follows:

  1. If the sensor tip has a black/sooty deposit, this may indicate a rich fuel mixture.
  2.  
  3. If the sensor tip has a white, gritty deposit, this may indicate an internal coolant leak.
  4.  
  5. If the sensor tip has a brown deposit, this could indicate oil consumption.
  6.  
  7. Turn the ignition switch to OFF.
  8.  
  9. Measure the resistance between the sensor and the connector terminals (terminals 2 and 5).
  10.  
  11. If measured value is more than 1 ohm, replace the sensor.
  12.  

Perform a visual inspection of the sensor as follows:

  1. If the sensor tip has a black/sooty deposit, this may indicate a rich fuel mixture.
  2.  
  3. If the sensor tip has a white, gritty deposit, this may indicate an internal coolant leak.
  4.  
  5. If the sensor tip has a brown deposit, this could indicate oil consumption.
  6.  
  7. On 2003-2004 vehicles, measure the resistance between the sensor and the connector terminals (connector B262/terminal 2 and connector B262/terminal 1) and (connector B262/terminal 3 and connector B262/terminal 4).
  8.  
  9. On 2005 vehicles, measure the resistance between the sensor and the connector terminals (terminals 1 and 6).
  10.  
  11. If measured value is more than 5 ohm, replace the sensor.

    Click image to see an enlarged view

    Fig. Front oxygen sensor connector location-Forester 2002 2.5L SOHC engine



    Click image to see an enlarged view

    Fig. Front oxygen sensor connector location-Forester 2003-2004 2.5L SOHC engine



    Click image to see an enlarged view

    Fig. Front oxygen sensor connector location-Forester 2005 2.5L SOHC engine

  12.  

Rear Sensor

Perform a visual inspection of the sensor as follows:

  1. If the sensor tip has a black/sooty deposit, this may indicate a rich fuel mixture.
  2.  
  3. If the sensor tip has a white, gritty deposit, this may indicate an internal coolant leak.
  4.  
  5. If the sensor tip has a brown deposit, this could indicate oil consumption.
  6.  
  7. Turn the ignition switch to OFF.
  8.  
  9. Disconnect the connectors from the sensor.
  10.  
  11. Turn the ignition switch ON.
  12.  
  13. On 1998-2001 vehicles, measure the voltage between the sensor harness connector and engine ground (connector E24 terminal 4+/engine ground -). If measured value is more than 0.2 volt, replace the sensor.
  14.  
  15. On 2002-2005 vehicles, measure the voltage between the sensor harness connector terminals (terminals 1 and 2). If measured value is more than 30 ohms, replace the sensor.

    Click image to see an enlarged view

    Fig. Rear oxygen sensor connector location-Forester 1998-2001 2.5L SOHC engine



    Click image to see an enlarged view

    Fig. Rear oxygen sensor connector location-Forester 2002-2004 2.5L SOHC engine



    Click image to see an enlarged view

    Fig. Rear oxygen sensor connector location-Forester 2005-2005 2.5L SOHC engine

  16.  

 
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