626 1999-2001

Heated Oxygen Sensor

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Operation



Specific to:

Mazda 626 1999-2002

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:

Mazda 626 1998-2002

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:

Mazda 626 1998-2002

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

Removal & Installation



Specific to:

Mazda 626 1999-2002


CAUTION
The temperature of the exhaust system is extremely high after the engine has been run. To prevent personal injury, allow the exhaust system to cool completely before removing sensor from the exhaust system.

  1. Disconnect the negative battery cable.
  2.  
  3. Raise and safely support the vehicle on jack stands.
  4.  
  5. Disconnect the HO2S from the engine control sensor wiring.
    NOTE
    If excessive force is needed to remove the sensors lubricate the sensor with penetrating oil prior to removal.

  6.  
  7. Remove the sensors with a sensor removal tool, such as Ford Tool T94P-9472-A or equivalent.
  8.  

To install:

  1. Install the sensor in the mounting boss, and then tighten it to 27-33 ft. lbs.
  2.  
  3. Connect the sensor electrical wiring connector to the engine wiring harness.
  4.  
  5. Lower the vehicle.
  6.  
  7. Connect the negative battery cable.
  8.  

Testing



2.0L 4-Cylinder Engine (FS)

Specific to:

Mazda 626 1998-2002

  1. Disconnect the PCM connector.
  2.  
  3. Connect a 104-Pin Breakout Box to the PCM
  4.  
  5. Tighten the connector bolt to 70-95 inch lbs. (8-10 Nm).
  6.  
  7. Warm up the engine to normal operating temperature.
  8.  
  9. Measure the voltage at PCM terminals 35 and 60.
  10.  
  11. Voltage for the front HO2S should be:

    Ignition ON: less than 1.0 volt
     
    At idle with engine cold: less than 0.5 volt
     
    At idle with engine warm: 0.1-0.9 volt
     
    On deceleration: 0-0.5 volt
     
    During acceleration: 0.5-1.0 volt
     

  12.  
  13. Voltage for the rear HO2S should be:

    Ignition ON: less than 1.0 volt
     
    At idle with engine cold: approximately 0.0 volt
     
    At idle with engine warm: 0.1-0.9 volt
     

  14.  
  15. If not as specified, inspect the following.

    Intake-air system
     
    Fuel system
     
    On-board diagnostic system
     
    Related harnesses
     

  16.  
  17. If these systems are okay, replace the heated oxygen sensor.
  18.  

Heated Oxygen Sensor Heater Inspection
  1. Disconnect the heated oxygen sensor connector.
  2.  
  3. Measure the resistance between heated oxygen sensor terminals C and D using an ohmmeter. It should be approximately 6.0 ohms.
  4.  
  5. If not as specified, replace the heated oxygen sensor.
  6.  
  7. If okay, inspect related harness or connectors.

    Click image to see an enlarged view

    Fig. Measure the resistance between heated oxygen sensor terminals C and D using an ohmmeter.

  8.  

2.5L V6 Engine (KL)

Specific to:

Mazda 626 1998-2002

  1. Disconnect the PCM connector.
  2.  
  3. Connect a 104-Pin Breakout Box to the PCM
  4.  
  5. Tighten the connector bolt to 70-95 inch lbs. (8-10 Nm).
  6.  
  7. Warm up the engine to normal operating temperature.
  8.  
  9. Measure the voltage at PCM terminal 60, 87, 35 and 61.
  10.  
  11. Voltage for the front HO2S at terminals 60 and 87 should be:

    Ignition ON: less than 1.0 volt
     
    At idle with engine cold: less than 0.5 volt
     
    At idle with engine warm: 0.1-0.9 volt
     
    On deceleration: 0-0.5 volt
     
    During acceleration: 0.5-1.0 volt
     

  12.  
  13. Voltage for the rear HO2S at terminals 35 and 61 should be:

    Ignition ON: less than 1.0 volt
     
    At idle with engine cold: approximately 0.0 volt
     
    At idle with engine warm: 0.1-0.9 volt
     
    On deceleration: approximately 0 volt
     
    During acceleration: approximately 0 volt
     

  14.  
  15. If not as specified, inspect the following.

    Intake-air system
     
    Fuel system
     
    On-board diagnostic system
     
    Related harnesses
     

  16.  
  17. If these systems are okay, replace the heated oxygen sensor.
  18.  

Heated Oxygen Sensor Heater Inspection
  1. Disconnect the heated oxygen sensor connector.
  2.  
  3. Measure the resistance between heated oxygen sensor terminals C and D using an ohmmeter.
  4.  
  5. Resistance should be as follows:

    Front HO2S (left or right side): approximately 3.3 ohms
     
    Rear HOS2 (left or right side): approximately 6.0 ohms
     

  6.  
  7. If not as specified, replace the heated oxygen sensor.
  8.  
  9. If okay, inspect related harness or connectors.

    Click image to see an enlarged view

    Fig. Measure the resistance between heated oxygen sensor terminals C and D using an ohmmeter.

  10.  

Heater Circuit

Specific to:

Mazda 626 1999-2002

  1. Disconnect the HO2S connector.
  2.  
  3. Measure the resistance between the HO2S terminals C and D. Standard value:
    1. Front sensor-3.0-3.6 ohms
    2.  
    3. Rear sensor-5.0-7.0 ohms
    4.  

  4.  
  5. If not as specified, replace the HO2S.
  6.  
  7. If within specifications, check connectors and wiring between the sensor and ECM/PCM.
  8.  

Oxygen Sensor Circuit

Specific to:

Mazda 626 1999-2002

  1. Warm up the engine and run it at idle.
  2.  
  3. Disconnect the HO2S connector.
  4.  
  5. Connect the voltmeter positive test lead terminal A and negative test lead to terminal B.
  6.  
  7. With the vehicle stopped, run the engine at 3,000 rpm until the voltmeter moves between 0.5 and 0.7 V.
  8.  
  9. Measurement the voltage changes when the engine speed increases and decreases suddenly several times. Standard value:
    1. Acceleration-0.5-1.0 volt
    2.  
    3. Deceleration-0-0.5 volt
    4.  

  10.  
  11. If not as specified, replace the HO2S.
  12.  
  13. If within specification, check wiring harness and connectors between HO2S and PCM.

    Click image to see an enlarged view

    Fig.



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    Fig.



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    Fig.



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    Fig.



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    Fig.



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    Fig.

  14.  

 
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