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Oxygen (O2) Sensor

  1. Start engine and warm to operating temperature. Disconnect oxygen sensor. Connect a DVOM between Purple lead of oxygen sensor and ground. Place meter on the 2-volt scale.
  2. Using another DVOM on the 20-volt scale, connect voltmeter in series between Purple wire from the ECM and the positive post of battery. This will simulate a rich condition, causing ECM to respond by leaning mixture. Reading on voltmeter connected to oxygen sensor should decrease to less than .3 volt.
  3. Move voltmeter lead from battery positive post to battery negative post. This will simulate a lean condition, causing ECM to respond by richening mixture. Reading on voltmeter connected to oxygen sensor should increase to greater than .8 volt. If reading does not change as specified, replace O2 sensor.
  4. If a second DVOM is not available, install a jumper in Purple wire from the ECM. Hold jumper in one hand and touch positive post of battery with other hand to simulate a rich condition. Touch negative post of battery to simulate a lean condition. For additional testing procedures, see appropriate G - TESTS W/ CODES article.
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