Sentra 2008

Heated Oxygen Sensor

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Location



Specific to:

Nissan Sentra 2007-2012



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Fig. The primary oxygen sensor (air/fuel ratio sensor) is in the intake manifold below the heat shield. 2.5L engine shown.

Operation



Specific to:

Nissan Sentra 2007-2012

Air fuel ratio (A/F) Sensor 1 is a planar one-cell current-limiting sensor. It is capable of precise measurement of lambda (-= 1), but it can also measure in the lean and rich ranges. The sensor element is composed of an electrode layer that carries voltage supplied by the ECM. A lean A/F ratio allows more oxygen to reach the sensor, which allows more current flow through the element, so more of the reference voltage is returned to the ECM. A rich A/F ratio inhibits current flow through the element, reducing sensor output voltage. A heater is integrated in the sensor element to ensure the required operating temperature of about 1,472°F (800°C).

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Fig. A/F sensor output voltage increases as oxygen increases

These sensors are also used to monitor catalyst efficiency and are called Sensor 2 (on California models, there may also a Sensor 3). They are mounted in the exhaust system downstream of the catalytic converter.

Removal & Installation



Specific to:

Nissan Sentra 2007-2012

  1. Make sure the exhaust manifold is cool.
  2.  
  3. Unplug the connector and remove the sensor with an oxygen sensor wrench or socket.
  4.  
  5. When installing, lightly coat the threads with anti-seize and torque to 23 ft. lbs. (31 Nm). Do not over tighten or the Malfunction Indicator Light (MIL) may turn on.
  6.  

Testing



Specific to:

Nissan Sentra 2007-2012

  1. Turn ignition switch OFF and wait at least 10 seconds before going to the next step.
  2.  
  3. Confirm that battery voltage is more than 11V with the engine at idle.
  4.  
  5. Start engine and warm it up to normal operating temperature.
  6.  
  7. Let it idle for 2 minutes and check for 1st trip DTC.
  8.  
  9. If the fault codes indicate oxygen sensor heater malfunction:
    WARNING
    Connect the voltmeter ground probe to engine or chassis ground. Do not test circuits with the meter connected to the battery or the ECM may be damaged.



    Turn the ignition switch OFF and unplug the sensor connector.
     
    With the ignition switch ON , check for battery voltage at terminal 3 on the wiring harness connector. This power comes through a fuse on the main fuse panel.
     



    With the ignition switch OFF , check continuity of the wiring harness between sensor terminal 4 and the ECM. Look for open circuits or short circuits to power. This is the sensor heater ground circuit.
     
    On the sensor itself, check resistance across terminals 3 and 4. On Sensor 1, heater resistance should be about 2 ohms at room temperature. On Sensor 2, heater resistance should be 3.3 to 4.4 ohms.
     

  10.  
  11. If the fault codes indicate sensor malfunction, connect a scan tool or oscilloscope and monitor oxygen sensor operation. Sensor 1 should output approximately 2.2 volts at steady no-load idle.
  12.  
  13. If the sensor does not perform correctly at idle or while driving, make sure the fuel injection and ignition systems are functioning properly and that the engine is mechanically sound.
  14.  
  15. If no other cause can be found for rich or lean operation, replace the sensor.
  16.  

 
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