How to quickly test an O2 sensor signal wire for opens and shorts when no scan data is available. This test is very useful in identifying wiring harness integrity when you have an oxygen sensor signal that is either fixed high or low. You can actually use your body as a resistor instead of a test light if that makes you more comfortable.

Engine Performance Diagnostics chapter 5 page 23

test shown enh 50

  • how to simulate a lean oxygen sensor signal
  • how to simulate a rich oxygen sensor signal

Tools used

  • test light
  • back-probing pins
  • lab scope
  • digital multimeter

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

Related videos:

O2 Sensor wiring quick tests (Ford with no bias voltage):


O2 sensor testing (fixed lean) P0174, P0154, P0155 - Mitsubishi:


Ford O2 Sensor Testing:


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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.

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