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Test TC-105A - Downstream O2 Sensor Heater Failure

NOTE: For connector terminal ID, see the CONNECTOR IDENTIFICATION DIRECTORY. For wiring diagram, see WIRING DIAGRAMS - 3.8L article.
  1. Using scan tool, check for stored Diagnostic Trouble Codes (DTCs). If DTCs exist that are related to the downstream oxygen sensor, refer to appropriate test for the specified DTC. If no DTCs exist that are related to the downstream oxygen sensor, go to next step.
  2. Turn ignition on with engine off. Wait 3 minutes and then use scan tool to monitor downstream oxygen sensor voltage for a few minutes. Once downstream oxygen sensor voltage stabilizes between .4 and .6 volt, use scan tool to actuate downstream oxygen sensor heater test while monitoring downstream oxygen sensor voltage for at least 2 minutes.
  3. If downstream oxygen sensor voltage still remains at .4-.6 volt, go to step 5). If downstream oxygen sensor voltage does not remain at .4-.6 volt, go to next step.
  4. Conditions required to set DTC are not present at this time. DTC may be stored in Powertrain Control Module (PCM) if no downstream oxygen sensor signal is received when PCM powers up the downstream oxygen sensor heater. Possible causes are: open heater element circuit, downstream oxygen sensor failure, defective PCM, defective connector terminals or wiring. Stop downstream oxygen sensor heater test. Test is complete. Perform TEST VER-5A.
  5. Disconnect connector at downstream oxygen sensor mounted on exhaust pipe, behind catalytic converter. Inspect connector for pushed out, miswired or damaged terminals. If terminals are pushed out, miswired or damaged, repair connector as necessary. Perform TEST VER-5A. If terminals are not pushed out, miswired or damaged, go to next step.
  6. Using voltmeter, check voltage at terminal No. 2 (Dark Green/Orange wire) on wiring harness side of connector for downstream oxygen sensor while still performing downstream oxygen sensor heater test.
  7. If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, repair open circuit in Dark Green/Orange wire from Auto Shutdown (ASD) relay. The ASD relay is located in power distribution center at driver's side front corner of engine compartment, near battery.
  8. Stop downstream oxygen sensor heater test. Using ohmmeter, check resistance of downstream oxygen sensor heater between terminals No. 1 and 2 (White wires) on oxygen sensor side of connector for downstream oxygen sensor. See Figure. If resistance is 4-7 ohms, go to next step. If resistance is not 4-7 ohms, replace downstream oxygen sensor. Perform TEST VER-5A.
  9. Using ohmmeter, check resistance between ground and terminal No. 1 (Black wire) on wiring harness side of connector for downstream oxygen sensor. If resistance is less than 5 ohms, replace downstream oxygen sensor. Perform TEST VER-5A. If resistance is 5 ohms or more, repair open circuit in Black wire and ground. Perform TEST VER-5A.
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