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Sub-Oxygen Sensor (LSi California)

  1. A malfunction in the sub-oxygen sensor circuit will set diagnostic trouble Code 27. For testing procedures, see TESTS W/CODES article in this section. Use following procedure to test sub-oxygen sensor.
  2. Start engine and warm to operating temperature. Disconnect sub-oxygen sensor. Connect a DVOM between lead of sub-oxygen sensor and ground. Place DVOM on the 2-volt scale. Voltmeter reading should increase to greater than .8 volt.
  3. Using another DVOM on the 20-volt scale, connect voltmeter in series between the sub-oxygen sensor wire from ECM and positive post of battery. Reading on voltmeter connected to sub-oxygen sensor should decrease to a low voltage (less than .3 volt).
  4. If a second DVOM is not available, install short jumper in sub-oxygen sensor wire from ECM. Hold jumper in one hand and touch positive post of battery with other hand. This should cause sub-oxygen sensor to produce less than .3 volt.
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