Use this test to quickly and accurately check the O2 sensor signal wire for an open or short to ground or verify a shorted O2 sensor.  A manufacturer flow chart will have you disconnect the O2, disconnect the engine computer (ECU, ECM, PCM) and then measure the signal wire for opens and shorts with an ohmmeter. Using the "bias voltage" test I am showing in this video, you can perform the same tests in a fraction of the time.

"Bias voltage" on a circuit can be difficult to understand from an engineering standpoint but it is super easy to use when you know it is there.

Engine Performance Diagnostics 5 pages 11-18

Tools used

  • lab scope
  • digital multimeter
  • back-probing tool

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(Chapters 4 and 5) Fuel Trim and Oxygen Sensor Testing

Related videos:

How to quickly test an oxygen sensor circuit (GM bias voltage) :


What can cause an O2 sensor to read near 5 volts? :


O2 sensor circuit testing (a ScannerDanner Premium lecture) :


WARNING! Aftermarket Oxygen Sensors (Chrysler part 1):


WARNING! Aftermarket Oxygen Sensors (Chrysler part 2) :


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For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available as an eBook or paper book.

Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium. There is a 14 day free trial.

On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!