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Test TC-103A - (Left) Upstream O2 Sensor Heater Failure

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION  Directory. For wiring diagram, see WIRING DIAGRAMS article.
NOTE: Vehicle is equipped with left and right upstream O2 sensor.
  1. Disconnect (left) upstream O2 sensor connector. Allow O2 sensor to cool to room temperature before checking resistance. Using an external ohmmeter, measure resistance between ASD relay output circuit and heater ground circuit (between 2 White wires) at (left) upstream O2 sensor connector (component side). See LEFT UPSTREAM O2 SENSOR CONNECTOR WIRE ID (COMPONENT SIDE) . If resistance is 4-6 ohms, go to next step. If resistance is not 4-6 ohms, replace (left) upstream O2 sensor. Perform TEST VER-5A.
  2. Using scan tool ohmmeter mode, check resistance of O2 sensor heater ground circuit at (left) upstream connector (harness side). See LEFT UPSTREAM O2 SENSOR CONNECTOR WIRE ID (HARNESS  SIDE). If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open heater ground circuit. Perform TEST VER-5A.
  3. Start engine. Using scan tool in voltmeter mode, check voltage of sensor ground circuit at (left) upstream O2 sensor connector (component side). See the LEFT UPSTREAM O2 SENSOR CONNECTOR WIRE ID TABLE (COMPONENT SIDE). If voltage is 5 volts or less, go to next step. If voltage is more than 5 volts, repair short to voltage on sensor ground circuit. Perform TEST VER-5A.
  4. With engine running, using scan tool in voltmeter mode, check voltage of ASD relay output circuit at (left) upstream O2 sensor connector (component side). See the LEFT UPSTREAM O2 SENSOR CONNECTOR WIRE ID (COMPONENT SIDE). If voltage is less than 12 volts, repair open ASD relay output circuit. Perform TEST VER-5A. If voltage is 12 volts or more, replace (left) upstream O2 sensor. Perform TEST VER-5A.
LEFT UPSTREAM O2 SENSOR CONNECTOR WIRE ID (COMPONENT SIDE)

Application Wire Color
O2 Sensor Signal Circuit Black
O2 Sensor ASD Relay Output Circuit White
O2 Sensor Heater Ground Circuit White
O2 Sensor Ground Circuit Gray
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