OT: how do you test an oxygen sensor

[rimcanyon]

I installed an oxygen sensor and fuel/air gauge in my old car, and it worked fine for a year. Then no output. The gauge comes on and initializes, but thats it. So I installed a new sensor. Same problem, no change. The vendor being Amazon, there is no way to contact the mfr. Hence this post. How can I test the oxygen sensor to see if it is actually working?

Here is a link to the gauge: https://www.amazon.com/gp/product/B09K71MNGY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[GregSY]

Good question...but since the new sensor doesn't make any difference, that suggests the gauge is bad.

 

[Ralph_P]

The sensor has to be at operating temperature to test the output and has a heating element to help it get to temperature sooner. The output voltage is less than one volt and fluctuates about once per second. Such as .8v to .3v - .7v to .4v etc. I doubt the sensor is the problem, they are pretty reliable.

 

[Bill D]

Heat it with a torch and see if the voltage changes from 0.1-1.0 volts as you heat and let cool.
BilL D

 

[BT Fabrication]

I installed an oxygen sensor and fuel/air gauge in my old car, and it worked fine for a year. Then no output. The gauge comes on and initializes, but thats it. So I installed a new sensor. Same problem, no change. The vendor being Amazon, there is no way to contact the mfr. Hence this post. How can I test the oxygen sensor to see if it is actually working?

Here is a link to the gauge: https://www.amazon.com/gp/product/B09K71MNGY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Measure if there is voltage across the sensor. ususally 0.1V all the way to 0.9V and fluxuating up and down.

 

[GregSY]

I don't understand these 'measure the voltage' comments. The sensor has no voltage by itself....so if you are going to measure voltage there needs to be 'further instructions' such 'connect the red wire to 12V positive and the black to 12V negative and measure the voltage with your meter connected to the yellow wire and the black wire.'

 

[MwTech Inc]

Ox sensors generate their own voltage, that is what the computer "reads"
Most sensors today are heated meaning they do apply voltage to an element in the sensor to get it warm quicker, an emissions thing
Allows the computer to start reading data sooner to adjust fuel.

 

[Bill D]

I believe it is some kind of thermocouple that generates a dc voltage relative to ambient air vs the metal mass inside the thrermocouple. It has to warm up to some minimum temperature difference to begin producing a measurable voltage. If it has three wires the third wire is a lead to a heating coil to preheat the thermocouple so it responds sooner . I assume there is a case ground lead that is unseen. Most car stuff has ground current to the frame or metal part. Antisieze for o2 senders has metal in it so it conducts electricity to the metal exhaust manifold. Regular grease base antisieze may not conduct electrical currents causing o2 sensor problems. Make sure the exhaust manifold has a good ground tied to the battery.
I believe a 02 sensor does not actually measure o2 levels. It is looking at exhaust temperature and knows if it is too low there is cooler unburned o2 in the exhaust stream.
Similar to how the human body does not react to O2 levels. We feel CO2 levels if they get too high and feel we need more fresh air. But if we breathe pure N2 with no o2 our lungs are happy until we pass out from lack of o2. never feeling we are out of breath.
Bill D

 

[janc]

Oxygen sensors of this type do measure the oxygen/carbon ratio, they are often a two wire affair, so grounding is not necessary. The element does need to be hot enough to give a proper reading, generally above .5V is carbon rich, while less than .5V is an oxidizing atmosphere.
Heating the element with something like a cigarette lighter should give you an instant response, and depending on what color the flame is, you should get a pretty good idea what is going on.

 

[MwTech Inc]

There are 1,2 and 4 wire o2 sensors that are the most common
The 1 is long gone, they found out real quick you cant grd to the pipe.
So along came the 2 wire ,has no connection to the body, just two sensor wires
Emissions got tighter so then they made 4 wire, which still has the sensor wires but added a standalone heater circuit
for the sole purpose to get the computer into closed loop soon as possible.
O2 sensors do measure the amount of O2 going down the pipe. The chemical makeup of the sensor does this.
That is why on cars with o2 sensors vacuum leaks after the mass airflow/throttle body are nasty.

 

[jim rozen]

His setup is an aftermarket linear sensor setup, different than the standard sensors that are OEM in cars, which switch voltage states rapidly right around stoichiometry mix. The amazon link says 'lifetime warranty' whatever that means. If you're trying to use a standard sensor it won't possibly work, otherwise check the wiring again. Sensors can be poisoned by things like leaded fuels.

Oxygen sensors aren't thermocouples, they're more or less batteries that use the oxygen in the gas stream as the electrolyte. Typically zirconium oxide chemistry.

 

[BT Fabrication]

I believe it is some kind of thermocouple that generates a dc voltage relative to ambient air vs the metal mass inside the thrermocouple. It has to warm up to some minimum temperature difference to begin producing a measurable voltage. If it has three wires the third wire is a lead to a heating coil to preheat the thermocouple so it responds sooner . I assume there is a case ground lead that is unseen. Most car stuff has ground current to the frame or metal part. Antisieze for o2 senders has metal in it so it conducts electricity to the metal exhaust manifold. Regular grease base antisieze may not conduct electrical currents causing o2 sensor problems. Make sure the exhaust manifold has a good ground tied to the battery.
I believe a 02 sensor does not actually measure o2 levels. It is looking at exhaust temperature and knows if it is too low there is cooler unburned o2 in the exhaust stream.
Similar to how the human body does not react to O2 levels. We feel CO2 levels if they get too high and feel we need more fresh air. But if we breathe pure N2 with no o2 our lungs are happy until we pass out from lack of o2. never feeling we are out of breath.
Bill D

it is an element that has to be heated over 800F to start to operate and function.
it takes a sample of the exhaust gas stream and there are microscopic pores in an element that only allows flow of oxygen molecules into the sensing chamber to take a sample of the oxygen content in the exhaust and compare it to the outside ambient O2 levels then less O2 internally creates less voltage saying the sensor is reading rich and there is excess fuel that needs more oxygen. then more O2 comes through and goes high voltage and saying its lean and all the fuel has used up and left over oxygen is in the exhaust and more fuel needs to be added.
there are also stochiometric sensors but those are not as common.
also there are wide band and narrow band sensors depending on the model year.