Oxygen Sensor Frequently Asked Questions
The oxygen sensor will not come out.
Soak the sensor thread area with a powerful penetrating lubricant. Starting and revving the engine should further aid in loosening the sensor by heating up the bung. If you are using an open end wrench, try an O2 socket. If this fails, try a long ratchet or breaker bar in conjunction with your socket to generate more torque. If you are still unsuccessful, heat the bung with a torch until cherry red and remove the sensor. After the sensor is removed, be sure to use a thread cleaner to clean up the bung threads. In some cases the threads will need to be repaired. This can be done with a thread repair kit (Walker Part # 88-832). Do not use an impact wrench to remove an O2 sensor, as you will most likely strip the threads in the bung. For any issues requiring the replacement or addition of a bung, Walker carries a full line of oxygen sensor bungs and plugs.
How many oxygen sensors does a particular vehicle have?
Our Find Your Part lookup at www.walkerproducts.com can give you specific sensor data for most applications. Modern cars can have up to 6 or more O2 sensors.
Are the rear oxygen sensors really necessary?
The role of the downstream sensors is to monitor the output and health of the catalytic converter. Removing them will take away this function, and produce a CEL (check engine light) or MIL (malfunction indicator light) on the vehicle.
I am getting a CEL/MIL and a . . . code. Do I need to replace the oxygen sensor?
Not necessarily. The oxygen sensor simply reports the data that it gathers. For example, if you are getting a lean mixture code, you may have a vacuum leak or a faulty fuel injector. Replacing the oxygen sensor will not fix this problem. You will just get the same code again.
Do I need to replace all of the sensors at once?
It is best to replace O2 sensors in pairs. For example, if you replace the downstream left sensor, you should also replace the downstream right.
However, on most vehicles produced since 1996, replacing one sensor (especially the front engine monitoring sensor) will cause the ECU to set a code for the other sensors. This is because the new sensor switching activity is much faster than that of the older aged sensors. It is probable that on most vehicles, the code will be set within 30-60 days AFTER the first sensor replacement.
What is the life expectancy of an oxygen sensor?
Heated oxygen sensors should be checked or replaced every 60,000 miles, while unheated oxygen sensors should be checked or replaced every 30,000 miles.
How can I test an oxygen sensor?
You can test the O2 sensor on a vehicle by first identifying the signal wire on the sensor. Secondly, by using a voltmeter with the scale set to 1 volt, the voltage will fluctuate between 200 and 800 millivolts or .2 to .8 volts on your meter. If the sensor’s reading is stalled in position, or switches abnormally high or low, your sensor has failed. If your results are inconclusive, it’s best to have your vehicle checked at a professional shop.
Note: This test will not work on Air Fuel or Wide Band sensors.
A second method is to connect some of the various testers available on the market directly to the oxygen sensor. This method is not as accurate, but can detect some of the sensor failures.
What is a California emissions sensor? How do I know if I need one?
A California emissions O2 sensor is meant for vehicles that are designed to meet California emission regulations. Such vehicles should have a sticker under the hood or on the driver’s door jamb that identify them.
What are the symptoms of a failing oxygen sensor?
Typically, a failing sensor will produce poor gas mileage, hesitation or stalling, and a CEL/MIL. However, the oxygen sensor is not the only cause of these symptoms.
