Test TC-103A - Left/Upstream O2 Sensor Heater Failure

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION DIRECTORY. For component location, see wiring diagram in the appropriate WIRING DIAGRAMS article. See following list.

4.0L, see: WIRING DIAGRAMS - 4.0L 6-CYL .
5.2L, see: WIRING DIAGRAMS - 5.2L V8 .
CAUTION: Allow Oxygen Sensor (O2S) to cool to room temperature before checking resistance.

Disconnect left/upstream O2S connector. Using an external ohmmeter, check resistance between O2S (component side), ASD relay output circuit (White wire) and heater ground circuit (White wire). See Figure. If resistance is not 4-6 ohms, replace left/upstream O2S and perform TEST VER-5A. If resistance is 4-6 ohms, go to next step.
Using scan tool in ohmmeter mode, check resistance of O2S connector, heater ground circuit (Black/Tan wire). If resistance is 5 ohms or more, repair open heater ground circuit and perform TEST VER-5A. If resistance is less than 5 ohms, go to next step.
Start engine. Using scan tool in voltmeter mode, check voltage on left/upstream O2S connector, ASD relay output circuit (Dark Green/Orange wire). If voltage is less than 12 volts, repair open ASD relay output circuit and perform TEST VER-5A . If voltage is 12 volts or more, go to next step.
Turn engine off. Using an external ohmmeter, check resistance of O2S signal circuit (Black/Orange wire) between O2S connector and PCM Black connector. If resistance is 5 ohms or more, repair open signal circuit and perform TEST VER-5A. If resistance is less than 5 ohms, go to next step.
Check resistance of O2S ground circuit (Black/Light Blue wire) between O2S connector and PCM Black connector. If resistance is 5 ohms or more, repair open ground circuit and perform TEST VER-5A . If resistance is less than 5 ohms, replace left/upstream O2S and perform TEST VER-5A.

NOTE: A break in test sequence occurs at this point. Sequence skips from TEST TC-103A to TEST TC-105A. No tests have been omitted.