Question about 2001 Nissan Altima

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How do you replace the oxygen sensors in a 2001 nissan altima?

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  • angelina26 Oct 01, 2009

    front, near radiator and downstream, car has over 100k and check engine light is on.

  • yadayada
    yadayada May 11, 2010

    and how do u know the problem is the sensors? the downstream sensor is what is known as a catalytic converter efficiency monitor, u may have a worn out catalytic converter, let me see the codes and i will give you some guidance on this before you poss throw away a $100 or so on un-needed parts.

  • yadayada
    yadayada May 11, 2010

    which ones



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  • Nissan Master
  • 2,984 Answers


  1. Start the engine and allow it to reach normal operating temperature, then turn the ignition switch OFF.
  2. Disconnect the negative battery cable.
  3. Open the hood and locate the Oxygen (O2S) sensor connector. It may be necessary to raise and safely support the vehicle for access to the sensor and its connector. NOTE: On a few models, it may be necessary to remove the passenger seat and lift the carpeting in order to access the connector for a downstream O2S sensor.
  4. Disengage the O2S sensor pigtail connector from the vehicle harness connector. NOTE: There are generally 2 methods used to mount an O2S sensor in the exhaust system: either the O2S sensor is threaded directly into the exhaust component (screw-in type) or the O2S sensor is retained by a flange and 2 nuts or bolts (flange type). WARNING
    To prevent damaging a screw-in type O2S sensor, if excessive force is needed to remove the sensor lubricate it with penetrating oil prior to removal. Also, be sure to protect the tip of the sensor. O2S sensor tips are very sensitive and may be easily damaged if allowed to strike or come in contact with other objects.
  5. Remove the sensor, as follows:
    • Screw-in type sensors — O2S sensors are usually designed with a permanently attached wiring pigtail. This allows the wiring harness and sensor connectors to be positioned away from the hot exhaust system. It may be necessary to use a socket or wrench that is designed specifically for this purpose. Before purchasing such a socket, be sure that you can't save some money by using a box end wrench for sensor removal.
    • Flange type sensors — Loosen the hold-down nuts or bolts and pull the sensor out of the exhaust component. Be sure to remove and discard the old sensor gasket, if equipped. You will need a new gasket for installation.
  6. Perform a visual inspection of the sensor. Black sooty deposits may indicate a rich air/fuel mixture, brown deposits may indicate an oil consumption problem, and white gritty deposits may indicate an internal coolant leak. All of these conditions can destroy a new sensor if not corrected before installation. To install:
  7. Install the sensor, as follows: NOTE: A special anti-seize compound is used on most screw-in type O2S sensor threads, and is designed to ease O2S sensor removal. New sensors usually have the compound already applied to the threads. However, if installing the old O2S sensor or the new sensor did not come with compound, apply a thin coating of electrically-conductive anti-seize compound to the sensor threads. WARNING
    Be sure to prevent any of the anti-seize compound from coming in contact with the O2S sensor tip. Also, take precautions to protect the sensor tip from physical damage during installation.
    • Screw-in type sensors — Install the sensor in the mounting boss, then tighten it securely.
    • Flange type sensors — Position a new sensor gasket on the exhaust component and insert the sensor. Tighten the hold-down fasteners securely and evenly.
  8. Reattach the sensor pigtail connector to the vehicle harness connector.
  9. Lower the vehicle.
  10. Connect the negative battery cable.
  11. Start the engine and ensure no Diagnostic Trouble Codes (DTC's) are set.

Fig. 1: Since sensor locations vary between vehicles, the first step in removal is to locate the O2S sensors (arrows)...

How do you replace the oxygen sensors in a 2001 - bb4d603.jpg
    Fig. 2: ... and the sensor connector (2), which is usually near the O2S sensor (1), but removed enough from the heat of the exhaust system
    Fig. 3: Disengage the sensor pigtail connector half from the vehiHow do you replace the oxygen sensors in a 2001 - a1433b0.jpg connector half

Posted on Oct 01, 2009

Testimonial: "thank you so much for the great details!"

  • Greg Bernett
    Greg Bernett Oct 01, 2009

    Fig. 4: For flange type sensors, loosen the hold-down fasteners...

    Fig. 5: ... which happen to be nuts in this particular case — some models may use bolts rather than nuts

    Fig. 6: Then, pull the sensor out of the exhaust component

    Fig. 7: For screw-in type sensors (arrow)...

  • Greg Bernett
    Greg Bernett Oct 01, 2009

    Fig. 8: ... either use a box end wrench to loosen the sensor or a socket designed expressly for this purpose...

    Fig. 9: ..., then remove the sensor from the exhaust component

    Hope this helps and please don't forget to rate!!!



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For O2 sensor visit

And run a scan.

Good luck.

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