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Test TC-103A - Upstream 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 upstream oxygen sensor, refer to appropriate test for the specified DTC. If no DTCs exist that are related to the upstream oxygen sensor, go to next step.
  2. Turn ignition on with engine off. Wait 3 minutes and then use scan tool to monitor upstream oxygen sensor voltage for a few minutes. Once upstream oxygen sensor voltage stabilizes between .4 and .6 volt, use scan tool to actuate upstream oxygen sensor heater test while monitoring upstream oxygen sensor voltage for at least 2 minutes.
  3. If upstream oxygen sensor voltage does not remain at .4-.6 volt, go to next step. If upstream oxygen sensor voltage remains at .4-.6 volt, go to step 6).
  4. If referred to this test from TEST TC-118A, return to TEST TC-118A and continue test procedure. If not referred to this test from TEST TC-118A, go to next step.
  5. Conditions required to set DTC are not present at this time. DTC may be stored in Powertrain Control Module (PCM) if no upstream oxygen sensor signal is received when PCM powers up the upstream oxygen sensor heater. Possible causes are: open heater element circuit, upstream oxygen sensor failure, defective PCM, dirt/moisture or grease inside connector, defective connector terminals or wiring, defective Auto Shutdown (ASD) relay. Stop upstream oxygen sensor heater test. Test is complete. Perform TEST VER-5A.
  6. Disconnect connector at upstream oxygen sensor mounted on the exhaust manifold. 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.
  7. Using voltmeter, check voltage at terminal No. 2 (Dark Green/Orange wire) on wiring harness side of connector for upstream oxygen sensor while still performing upstream oxygen sensor heater test.
  8. 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. Perform TEST VER-5A.
  9. Stop upstream oxygen sensor heater test. Using ohmmeter, check resistance of upstream oxygen sensor heater between terminals No. 1 and 2 (White wires) on oxygen sensor side of connector for upstream oxygen sensor. See Fig 1. If resistance is 4-7 ohms, go to next step. If resistance is not 4-7 ohms, replace upstream oxygen sensor. Perform TEST VER-5A.
    Fig 1: Checking Oxygen Sensor Heater Resistance
    G95D35058
  10. Using ohmmeter, check resistance between ground and terminal No. 1 (Black wire) on wiring harness side of connector for upstream oxygen sensor. If resistance is less than 5 ohms, replace upstream 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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