Subaru Car 1998-05

Heated Oxygen Sensor 1

Print

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.

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.

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



2.0L & 2.5L SOHC Engines
  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.  

2.2L Engines
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the necessary components to gain access to the sensor.
  4.  
  5. Disconnect the clip fastening the harness, if equipped.
  6.  
  7. Disconnect the connector.
  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.  

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.  

  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.  

  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. On front sensor, disconnect the connectors from the engine hanger and the front sensor.
  4.  
  5. Disconnect the connector from the rear sensor.
  6.  
  7. Raise and support the vehicle safely.
  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.  

Front Sensor
2.2L Engine
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the necessary components to gain access to the sensor.
  4.  
  5. Disconnect the clip fastening the harness, if equipped.
  6.  
  7. Disconnect the connector.
  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.  

2.5L DOHC Engine
  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.  

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.  

3.0L Engine
  1. Disconnect the negative battery cable.
  2.  
  3. Raise and support the vehicle safely.
  4.  
  5. Disconnect the connector.
  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 15.2 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. on all engines except the 3.0L engine. On the 3.0L engine, tighten the sensor to 15.2 ft. lbs.
  4.  

Testing



2.0L 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. Turn the ignition switch to OFF.
  8.  
  9. Measure the resistance between the sensor and the connector terminals (terminals 2 and 1).
  10.  
  11. If measured value is more than 5 ohm, replace the sensor.
  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. If, measured resistance between the sensor connector terminals is more than 30 ohms, replace the sensor.
  10.  

2.2L 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. Turn the ignition switch OFF.
  10.  
  11. Connect the Subaru scan tool. Start the engine. Turn the tool ON.
  12.  
  13. Allow the engine to reach 160 degrees F. Keep the engine speed at 2000-3000 rpm-s for one minute.
  14.  
  15. Read the data from the tool.
  16.  
  17. Iif the reading is equal to or more than 0.85 and equal to less than 1.15 in idling, replace the sensor.
  18.  

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. Turn the ignition switch OFF.
  10.  
  11. Connect the Subaru scan tool. Start the engine. Turn the tool ON.
  12.  
  13. Allow the engine to reach 160 degrees F. Keep the engine speed at 2000-3000 rpm-s for one minute.
  14.  
  15. Read the data from the tool.
  16.  
  17. If the reading is more than 0.1 volt between the value of max. output and min. output, replace the sensor.
  18.  

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. Measure the voltage between the sensor harness connector and the ECM (connector T6 terminal 4+/engine ground -). If measured value is more than 0.2 volt, replace the sensor.
  14.  

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. Measure the voltage between the sensor harness connector and engine ground (connector E25 and terminal 4+/engine ground -). If measured value is more than 0.2 volt, replace the sensor.
  14.  

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. Turn the ignition switch to OFF.
  8.  
  9. Disconnect the connectors from the ECM and the sensor.
  10.  
  11. Measure the resistance of the harness between the ECM and the sensor (connector B134 terminal 26/connector B18 terminal 3 and connector B134 terminal 33/connector B18 terminal 4).
  12.  
  13. If measured value is less than 1 ohm, replace the sensor.

    Click image to see an enlarged view

    Fig. Front oxygen sensor connector location-Baja 2.5L DOHC engine

  14.  

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-Impreza 2.5L DOHC engine

  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. 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-Legacy and Outback 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. Using the Subaru scan tool, read the sensor signal data. If the measured value is not within 0.2-0.4 volt, replace the sensor.

    Click image to see an enlarged view

    Fig. Rear oxygen sensor connector location-Baja 2.5L DOHC engine

  8.  

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-Impreza 2.5L DOHC engine

  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. 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-Legacy and Outback 2004-2005 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. Turn the ignition switch to OFF.
  8.  
  9. Disconnect the connectors from the ECM and the sensor.
  10.  
  11. Measure the resistance of the harness between the ECM and the sensor (connector B136 terminal 13/connector E18 terminal 1 and connector B136 terminal 22/connector B18 terminal 2).
  12.  
  13. If measured value is less than 1 ohm, replace the sensor.

    Click image to see an enlarged view

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

  14.  

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. Measure the resistance between the ECM and chassis ground (connector B136 and terminal 6, connector B136 and terminal 7, connector B136 and terminal 19, connector B136 and terminal 20).
  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. Turn the ignition switch to OFF.
  8.  
  9. On 2002 vehicles, measure the resistance between the sensor and the connector terminals (terminals 2 and 5).
  10.  
  11. On 2003-2004 vehicles, measure the resistance between the sensor and the connector terminals (terminals 3 and 4).
  12.  
  13. If measured value is more than 10 ohm, replace the sensor.
  14.  

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 between the sensor and the connector terminals (terminals 3 and 4).
  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-Impreza 1998-2001 2.5L SOHC engine



    Click image to see an enlarged view

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



    Click image to see an enlarged view

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



    Click image to see an enlarged view

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

  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. 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. Check the exhaust system for defects.
  8.  
  9. If equipped with manual transaxle, replace the sensor, as required.
  10.  
  11. If equipped with automatic transaxle, turn the ignition switch to OFF. Disconnect the connectors from the ECM and the sensor. Measure the resistance of the harness between the ECM and the sensor connector (Connector B136 terminal 6 and connector E18 and terminal 1. Connector B136 terminal 7 and connector E18 and terminal 6. Connector B136 terminal 19 and connector E18 and terminal 3. Connector B136 terminal 20 and connector E18 and terminal 4. If measured value is less than 10 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. 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 10 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. Measure the resistance between the ECM and chassis ground (Connector B136 terminal 13 and ground. Connector B136 terminal 22 and ground).
  8.  
  9. If measured value is more than 1 Mohm, replace the sensor.
  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 OFF.
  8.  
  9. Disconnect the connectors from the ECM and the sensor connector.
  10.  
  11. On 2005 vehicles, measure the resistance between the ECM and the sensor (Connector B134 terminal 33 and ground. Connector B134 terminal 26 and ground).
  12.  
  13. If measured value is more than 1 Mohm, replace the sensor.

    Click image to see an enlarged view

    Fig. Front oxygen sensor connector location-Legacy 1997-2000 2.5L SOHC engine with manual transaxle



    Click image to see an enlarged view

    Fig. Front oxygen sensor connector location-Legacy 1997-2000 2.5L SOHC engine with automatic transaxle



    Click image to see an enlarged view

    Fig. Front oxygen sensor connector location-Legacy 2001 2.5L SOHC engine with manual transaxle



    Click image to see an enlarged view

    Fig. Front oxygen sensor connector location-Legacy 2001 2.5L SOHC engine with automatic transaxle



    Click image to see an enlarged view

    Fig. Front oxygen sensor connector location-Legacy and Outback 2002 2.5L SOHC engine



    Click image to see an enlarged view

    Fig. Front oxygen sensor connector location-Legacy and Outback 2003-2004 2.5L SOHC engine



    Click image to see an enlarged view

    Fig. Front oxygen sensor connector location-Legacy and Outback 2005 2.5L SOHC engine

  14.  

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. Measure the voltage between the sensor harness connector and engine ground (connector T6 terminal 4+/engine ground -).
  14.  
  15. If measured value is within 0.2-0.5 volt, replace the sensor.

    Click image to see an enlarged view

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

  16.  

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. On 1998-2001 vehicles, turn the ignition switch ON.
  12.  
  13. On 1998-2001 vehicles, measure the voltage between the sensor harness connector and engine ground (connector E25 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-Impreza 1998-2001 2.5L SOHC engine



    Click image to see an enlarged view

    Fig. Rear oxygen sensor connector location-Impreza 2002-2003 2.5L SOHC engine



    Click image to see an enlarged view

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



    Click image to see an enlarged view

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

  16.  

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 engine OFF.
  8.  
  9. Connect the Subaru scan tool. Start the engine. Turn the tool ON.
  10.  
  11. Allow the engine to reach 160 degrees F. Keep the engine speed at 2000-3000 rpm-s for one minute.
  12.  
  13. Read the data from the tool.
  14.  
  15. If the reading is not fixed between 0.2-0.4 volt, replace the sensor.
  16.  

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. On 2001 vehicles, turn the ignition switch ON.
  12.  
  13. On 2001 vehicles, measure the voltage between the sensor harness connector and engine ground (connector T6 terminal 4+/engine ground -). If measured value is more than 0.2 volt, replace the sensor.
  14.  
  15. On 2002-2003 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.
  16.  
  17. On 2004 vehicles, measure the voltage between the sensor harness connector and engine ground (connector T6 terminal 4+/engine ground -). If measured value is within 0.2-0.5 volt, replace the sensor.
  18.  
  19. On 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-Legacy 1997-2000 2.5L SOHC engine



    Click image to see an enlarged view

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



    Click image to see an enlarged view

    Fig. Rear oxygen sensor connector location-Legacy and Outback 2002-2004 2.5L SOHC engine



    Click image to see an enlarged view

    Fig. Rear oxygen sensor connector location-Legacy and Outback 2005 2.5L SOHC engine

  20.  

 
label.common.footer.alt.autozoneLogo