Oxygen Sensor (O2) – Testing And Replacement


Oxygen Sensor (O2)

One of the most important sensors in modern cars is the oxygen sensor (commonly referred to as the (O2) sensor).

If your oxygen sensor (O2) fails to function properly, your engine management computer cannot determine the air to fuel ratio.

Therefore, the engine is forced to guess how much fuel to use, resulting in a polluted and poorly running engine.

So, Before we begin any oxygen sensor (O2) or lets get more information about them.

Oxygen sensors (O2) are mounted in the exhaust stream and monitor the content of the exhaust gases as they make their way through the system.

The (O2) sensor sends a signal back to the engine computer, informing it of the oxygen content in the exhaust stream.

The computer then uses this information to determine fuel metering and ensuring the catalytic converters are functioning properly.

On many vehicles, the oxygen sensor (O2) can last the entire life cycle of the car, but on many others the sensor can fail before 100,000 or so miles.

A faulty (O2) sensor will result in:

  • Excessive fuel consumption
  • Poor power and acceleration
  • Rough idle
  • Rich fuel mixture and black smoke
  • Trouble code and an illuminated Check Engine Light
Compare Oxygen Sensors
Compare Oxygen Sensors

Older vehicles had a single (O2) sensor in the engine compartment, closer to the exhaust manifold. Most newer vehicles have more than one (and as many as four), with the second sensor farther down the exhaust pipe, closer to the catalytic converter. There are a few (O2) sensor codes, including P0030 to P0064 and P0130 to P0167. The code that’s registered should tell you the specific sensor that has failed.

If you need help on further testing to confirm the problem, Follow the link below:


If you’ve determined that a (O2) sensor has failed on your engine, it’s not that hard to change this part.

Removing The Failed (O2) Sensor

  1. First disconnect the negative battery cable.
  2. Now, raise the vehicle if you need to.
  3. Unplug the sensors electrical connector carefully to avoid breaking the plastic locking tabs.
  4. Then, turn the sensor counterclockwise using an oxygen sensor socket. This sensor socket has a slit on one side to fit the sensors wiring harness through during removal or installation.
  5. If the sensor seems frozen in place or seized, stop. Cut the wiring harness off the sensor and use a six-point deep well socket (or spark plug socket of the correct size, usually a 7/8-inch socket) and a ratchet or breaker bar instead.
  6. Apply penetrating oil to the base of the sensor, following the instructions on the product’s label.
  7. Try to turn the sensor just a few degrees counterclockwise, just until the sensor refuses to move anymore.
  8. Apply penetrating oil to the base of the sensor and tighten it again, turning the sensor clockwise.
  9. Repeat steps 5 and 6 as many times as necessary. Remember not to force the sensor loose. Just turn the unit counterclockwise until the sensor refuses to move. Apply penetrating oil and tighten it again. Gradually, the sensor will begin to come loose.
  10. Once you’ve removed the sensor, apply penetrating oil to the boss (mounting) threads in the exhaust manifold, tube or catalytic converter, and clean the threads using a nylon brush.
  11. Closely check the boss threads. If the threads seem nicked, a bit flattened or have some other minor damage, use a thread chaser to repair the threads. However, if the threads seem crushed or stripped, use a tap to repair them. Check a drill and tap size chart to get the correct tap size for the job.
  12. After the repair, thoroughly clean up the threads of any metal shavings using penetrating oil and a clean rag.

Never force a seized (O2) sensor or you’ll end up with a much more expensive repair.

Oxygen Sensor
Oxygen Sensor

Installing The New (O2) Sensor

  1. After removing the old sensor, compare it to the new one; or bring the old sensor with you when you buy the new one to make sure they are the same. If possible, try to replace it with an OEM unit instead of a “universal” type. Otherwise, you may need to cut off the electrical connector from the old (O2) sensor and splice it to the new (O2) sensor.
  2. If the new sensor doesn’t come with it, apply a dab of anti-seize compound to a small spot on the threads. This will help you remove it when its service schedule comes up again.
  3. When handling the new sensor, do not touch the tip or contaminate it with oil, grease, dirt or any other kind of foreign matter. Contamination will cut short the new sensors service life.
  4. To prevent cross threading start screwing in the sensor by hand.
  5. Using an oxygen sensor socket and a torque wrench, tighten the sensor to the torque listed in your service manual. If you don’t have the manual, buy an inexpensive, aftermarket repair manual from your local auto parts store or online.
  6. Plug in the sensors electrical connector.
  7. Route and secure the wiring away from hot surfaces.
  8. Now, lower your vehicle, if you had to raise it, and reconnect the negative battery cable.

Oxygen Sensor (O2)-Conclusion

So, learning how to test and replace an (O2) sensor yourself can save you time and money. Also, doing it the correct way will save you from doing further damage.

Finally, Do not use an impact wrench to remove an (O2) sensor, as you will most likely strip the threads in the bung.

Worst case, If you do damage it there are many repair kits available online.

Good Luck !

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