How to test the Oxygen sensor?

Hello,

The oxygen sensor can be tested by observing the voltage fluctuation.
You will need to use a voltmeter to get started. It will require you to start the vehicle for about 15 minutes for everything to go to operating temperature. Then use the voltmeter to measure the voltage.

Here is a helpful guide that explains exactly what needs to be done:

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

Let me know of any questions.
Thank you.