Nissan Maxima 1993-1998 Repair Guide

Oxygen Sensor

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OPERATION



See Figure 1



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Fig. Fig. 1: Cutaway view of a heated oxygen sensor

The oxygen sensor supplies a signal to the ECM, which indicates a rich or lean condition during engine operation. The input data assists the computer in determining the proper air/fuel ratio. A low voltage signal from the sensor indicates too much oxygen in the exhaust (lean condition) and a high voltage signal indicates too little oxygen in the exhaust (rich condition).

Oxygen sensors are located in the exhaust system, usually in the exhaust manifold or near the catalytic converter. Heated oxygen sensors are used on some models to allow the engine to reach the closed loop state faster.

TESTING



Sensor

The ECM contains an oxygen sensor monitor function which is used to test the oxygen sensor.

  1. Locate the ECM and take note of the LED and mode switch positions.
  2.  
  3. Turn the ignition switch ON .
  4.  
  5. Turn the mode switch screw fully clockwise.
  6.  
  7. Wait at least 2 seconds.
  8.  
  9. Turn the mode switch screw fully counterclockwise.
  10.  
  11. Start the engine and allow it to reach operating temperature.
  12.  
  13. Run the engine at approximately 2000 rpm for 2 minutes under no load.
  14.  
  15. Ensure that the red LED on the ECM or the Malfunction Indicator Lamp (MIL) on the dashboard flash on and off more than 5 times every 10 seconds.
  16.  
  17. If the red LED on the ECM or the MIL do not function as specified, check the oxygen sensor circuit back to the ECM for continuity.
  18.  
  19. If continuity exists, the oxygen sensor may be faulty.
  20.  

Sensor Heater
FRONT

See Figure 2



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Fig. Fig. 2: Front oxygen sensor heater's terminal testing locations

  1. Disconnect the sensor electrical harness.
  2.  
  3. Measure resistance between the outer terminals of the connector.
  4.  
  5. Resistance should be 2.3-4.3 ohms @ 77°F (25°C).
  6.  
  7. Check continuity between the center terminal and each of the outer terminals. Continuity should not exist.
  8.  
  9. If resistance is not as specified or continuity exists, the oxygen sensor is faulty.
  10.  
  11. If resistance and continuity are within specification, check and repair the circuits.
  12.  

REAR

See Figures 3 and 4



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Fig. Fig. 3: Three-terminal rear oxygen sensor heater's terminal testing locations



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Fig. Fig. 4: Four-terminal rear oxygen sensor heater's terminal testing locations. Check resistance (top) and continuity (middle and bottom)

  1. Disconnect the sensor electrical harness.
  2.  
  3. On models with a three-terminal connector, measure resistance between the two outer terminals. On models with a four-terminal connector, measure resistance between the two illustrated terminals.
  4.  
  5. For three-terminal connectors, the resistance should be 5.2-8.2 ohms @ 77°F (25°C). For four-terminal connectors, the resistance should be 2.3-4.3 ohms @ 77°F (25°C).
  6.  
  7. On models with a four-terminal connector, also check continuity between the various terminal combinations, as illustrated. Continuity should not exist.
  8.  
  9. If resistance is not as specified or continuity exists, the oxygen sensor is faulty.
  10.  
  11. If resistance and continuity are within specification, check and repair the circuits.
  12.  

REMOVAL & INSTALLATION



See Figures 5, 6 and 7

Oxygen sensors are located in the exhaust manifold and may also be located in the exhaust system near the catalytic converter.

  1. Raise and support the vehicle safely, as required.
  2.  
  3. Label and disconnect the oxygen sensor electrical harness.
  4.  



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Fig. Fig. 5: Be sure to use the proper size wrench when removing the sensor from the exhaust system



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Fig. Fig. 6: Some oxygen sensors have a considerable length of wire; follow the wire to the connector

Lubricate the sensor threads with penetrating oil prior to removal.

  1. Remove the sensor using a box end wrench or special oxygen sensor socket.
  2.  

To install:
  1. Thread the sensor into the mounting boss and tighten to 30-37 ft. lbs. (40-50 Nm).
  2.  

Most new oxygen sensor threads are coated with anti-seize compound. If you are reinstalling a used oxygen sensor, carefully coat the threads with anti-seize compound. Take care not to allow the oxygen sensor element to be contaminated by the compound.



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Fig. Fig. 7: Be sure to coat the threads of the oxygen sensor with anti-seize compound before installation

  1. Connect the engine control electrical harness to the sensor.
  2.  
  3. If applicable, lower the vehicle.
  4.  

 
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