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Test TC-105A - 1/2 O2 Sensor Heater Failure

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION DIRECTORY. For component location see wiring diagram in the WIRING DIAGRAMS article.
NOTE: 1/2 HO2S is located in downstream position. On models equipped with 4 HO2S, 1/2 HO2S is located in left downstream position.
NOTE: Allow HO2S to cool to room temperature before checking resistance.
  1. Using scan tool, read DTCs. Repair any other HO2S related DTCs before proceeding. Turn ignition on, engine off. Wait 3 minutes. Using scan tool in SENSORS, monitor 1/1 HO2S voltage. Wait for voltage to stabilize at more than 4.5 volts. Go to next step.
  2. Using scan tool in ACTUATOR TESTS, perform HO2S heater test. Monitor 1/2 HO2S voltage for 3 minutes. If voltage is more than one volt, go to step 4). If voltage is one volt or less, go to next step.
  3. Condition required to set DTC is not present at this time. O2 SENSOR HEATER FAILURE DTC sets if Powertrain Control Module (PCM) senses HO2S voltage at more than 3 volts for 30 to 90 seconds after a cold engine start. Possible causes are: open HO2S heater element circuit, HO2S failure, HO2S heater wiring failure, PCM failure, defective connections or wiring. Stop all actuator tests. Test is complete
  4. Disconnect 1/2 HO2S connector. Inspect connector and terminals for damage. Repair connector and terminals as necessary and perform TEST VER-5A. If connector and terminals are okay, go to next step.
  5. Ensure scan tool is actuating HO2S heater test. Using an external voltmeter, check voltage on HO2S ASD relay output circuit (Dark Green/Black wire). If voltage is 10 volts or less, repair open ASD relay output circuit and perform TEST VER-5A. If resistance is more than 10 volts, go to next step.
  6. Stop all actuator tests. Using an external ohmmeter, check resistance between HO2S (component side), ASD relay output circuit (White wire) and heater ground circuit (White wire). See Figure. If resistance is not 4-7 ohms, replace 1/2 HO2S and perform TEST VER-5A. If resistance is 4-7 ohms, go to next step.
  7. Check resistance between ground and HO2S connector, heater ground circuit (Black 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, replace 1/2 HO2S and perform TEST VER-5A.
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