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Home >> Geo >> 1995 >> Prizm LSi, 1.8 8, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests - 1.8L >> Computerized Engine Controls >> Engine Sensors & Switches >> Sub-Heated Oxygen Sensor (Sub-HO2S)
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Sub-Heated Oxygen Sensor (Sub-HO2S)

  1. A malfunction in the sub-HO2S circuit will set DTC 27. For testing procedures, see TESTS W/CODES - 1.8L article. Use following procedure to test sub-HO2S.
  2. Sub-HO2S is located after Three Way Convertor. A heater is used to promote activation of O2S. A voltage is produced in response to amount of Oxygen in exhaust gases. A lean mixture (high oxygen content) will produce a low voltage of approximately 0.1 volt. A rich mixture (low oxygen content) will produce a high voltage of approximately 0.9 volt.
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