How to Test an Oxygen or O2 Sensor - Plus a Quick Guide on What Each Sensor Wire is For

Absolutely great demo on o2 sensor. Was ASE cert mech for 25 yrs. Often found mechanics/teachers made assumptions on trainees basic knowledge. It was impressive you took the time to give detailed explanation. You would make a great teacher. Wish I had you as a forman when I had my shop. Don't think you were born yet. Lol Thank you

Been a tech 50 years. Best and simplest explanation I’ve heard!!! Great job!!!!

I think you did a good job of explaining and keeping the methods and results in perspective! It may not catch all problems but it will save lots of $ for lots of folks.

Great video! Finally found a video that explained what the wires are and differences between them and how to bench test them. Great job!

Thanks for the info. Very helpful. just in case no one has mentioned it, the heating effect of a resistance is Watts=(volts x volts) / Resistance. For a 7.2ohm resistance on a 12volt system this is 20Watts. This is a low heating effect, but added to the heat from the exhaust gases I guess it will achieve a two to three hundred degrees celsius.

I always recommend my subs to your channel when they asks what other Automotive YouTubers they should check out. Awesome video

this is a great explanation, the heater resistance is round about 4 ohms but does vary slightly from sensor to sensor, the sensor reading will rapidly change once the sensor is fully heated all the way around, using the blowtorch is definitely a near as damn it simulation of what the sensor will be experiencing in the exhaust manifold, this is a great way to test an existing sensor and a brand new one before fitting it, it is also a good idea to check the resistance reading of the sensor wires as there should be no resistance reading across it, if it does have resistance then it means that there is carbon crud bridging the sensor wire itself and this build up on an old sensor will cause false readings to the ecu.

Thank you for your videos. They are easy to understand and have been a great help! Good job!

Great video, really helps me! I'm chasing a P2195 (Oxygen Sensor Biased/Stuck Lean, Bank 1, Sensor 1)  on my Ford Focus. I've eliminated all other possible causes (vac leaks, exhaust leaks, etc) and have been scratching my head. I replaced my upstream sensor before anything, but I used the cheapest one I could find. This might be my problem, so I'm doing this procedure to check it. Thanks from a new subscriber!

A scan tool is the best way to test it with the O2 sensor(s) in situ. If it's both a code reader & one that scans live data,then it will tell you if the sensor is at fault or whether they are reporting a lean mixture due to an air leak or bad fuel pressure. For example , code for a MAF meter & an O2 sensor reporting a lean mixture will tell you that you may have an air leak.

An analog meter with a needle would show if the sensor has a faster reaction. That's the downside of the digital multi meters, you're not only looking at how fast the component is switching, the digital meter has a limited refresh rate.

Finally a down to the point video. Thank you.

Wells tech published VHS tapes on this method back in the OBD1 days, and I found the same thing as you - during testing of sensors that were "sluggish", the heat from the flame (making the o2 sensor cherry red) literally burned off deposits, and "fixed" sluggish sensors (sort of like the self-clean cycle in your kitchen oven). During normal operation, EGT's on a gasoline engine don't get hot enough to burn off these deposits that can foul a sensor over time... but your torch with the pinpoint flame can, and the test procedure itself "fixes" many of the sensors that trip an OBD code for "sluggish", or "slow response". Obviously not going to fix an "open heater" though...BTW - don't bang on the exhaust pipe, or use a hammer on your wrench, or drop the sensor when removing it...or you WILL have an open heater circuit by the time you want to reinstall it... ask me how I know...

Thanks just learned something new

Your videos are always so good. Thanks!

Well done. simple and direct and low cost. Greetings from downunder oz

I used the four wire explanation and parts and found two bad sensors. And better to hold torch below sensor head to create a fire shield rather to one side around sensor head! Thanks for taking time to educate the public.

Very informative. Thanks a lot!

Finaly someone that properly explains each wire.!

Great! Video I always wondered how to test O2 sensors. Just subbed. 👍