Test TC-103A - Upstream O2 Sensor Heater Failure

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION Directory. For wiring diagram, see WIRING DIAGRAMS article.

NOTE: 2.0L is equipped with one upstream O2 sensor.

Disconnect 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 upstream O2 sensor connector (component side). See the 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 upstream O2 sensor. Perform TEST VER-5A.
Using scan tool ohmmeter mode, check resistance of O2 sensor heater ground circuit at upstream connector (harness side). See 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.
Start engine. Using scan tool in voltmeter mode, check voltage of sensor ground circuit at upstream O2 sensor connector (component side). See the UPSTREAM O2 SENSOR CONNECTOR WIRE ID (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.
With engine running, using scan tool in voltmeter mode, check voltage of ASD relay output circuit at upstream O2 sensor connector (component side). See the 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 upstream O2 sensor. Perform TEST VER-5A.

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