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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> Engine Performance >> Testing & Diagnosis >> Engine Controls Self-Diagnostics - 4.3L >> Diagnostic Tests >> DTC P0140: Ho2S Circuit - Insufficient Activity - Bank 1, Sensor 2 >> Diagnostic Procedures

Diagnostic Procedures

  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
    2. NOTE: Allow the engine to cool for one-half hour before proceeding with this diagnostic. This allows the HO2S signal voltage to return to bias voltage, approximately 447 mV.
  2. Turn OFF the ignition. Install a scan tool. Turn ON the ignition, with the engine OFF. Command the HO2S heater ON with a scan tool. Observe the affected HO2S voltage for 2 minutes. Does the HO2S voltage go from bias voltage to more than or less than 300-600 mV? If yes, go to next step. If no, go to step  5.
  3. Start the engine. Allow the engine to reach operating temperature. Change the TP more than 5 percent within 1 second, 6 times. Observe the HO2S voltage with a scan tool. Is the HO2S voltage outside 400-499 mV? If yes, go to next step. If no, go to step  5.
  4. Observe the Freeze Frame/Failure Records data for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC or as close to the Freeze Frame/Failure Records data that you observed. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  5. Turn OFF the ignition. Disconnect the affected HO2S connector. Probe the HO2S low reference circuit with a test lamp that is connected to battery positive. Does the test lamp illuminate? If yes, go to next step. If no, go to step  9.
  6. Jumper the HO2S high signal circuit to the low reference circuit. Turn ON the ignition, with the engine OFF. Observe the HO2S voltage with a scan tool. Is the HO2S voltage less than 200 mV? If yes, go to step  10. If no, go to next step.
  7. Turn OFF the ignition. Disconnect the PCM connector containing the HO2S high signal circuit. Test the HO2S high signal circuit for an open. Did you find and correct the condition? If yes, go to step  22. If no, go to next step.
  8. Test the low reference circuit for an open between terminal "A" of the affected sensor harness connector and PCM terminal C1-28. Did you find and correct the condition? If yes, go to step  22. If no, go to step  18.
  9. Disconnect the PCM connector containing the HO2S low reference circuit. Test the low reference circuit for an open between terminal "A" of the affected sensor harness connector and PCM terminal C1-63. Did you find and correct the condition? If yes, go to step  22. If no, go to step  18.
  10. Remove the jumper from the previous step. Is the ENG 1 fuse (Astro and Safari) or the OXYSEN fuse (Blazer, Jimmy Canadian, Sonoma and S10 Pickup) open? If yes, go to step  13. If no, go to next step.
  11. Turn ON the ignition, with the engine OFF. Probe the HO2S ignition 1 voltage circuit with a test lamp that is connected to a good ground. Does the test lamp illuminate? If yes, go to next step. If no, go to step  19.
  12. Connect a test lamp between the affected HO2S ignition 1 voltage circuit and the HO2S heater low control circuit. Turn ON the ignition, with the engine OFF. Command the HO2S heater ON with a scan tool. Does the test lamp illuminate? If yes, go to step  17. If no, go to step  16.
  13. Test the HO2S ignition 1 voltage circuit for a short to ground. Replace the OXYSEN fuse. Did you find and correct a short to ground in the ignition 1 voltage circuit? If yes, go to step  22. If no, go to next step.
  14. Test the HO2S ignition 1 voltage circuit, sensor side, for a short to the HO2S body. Did you find the condition? If yes, go to step  20. If no, go to next step.
  15. Measure the resistance between the HO2S ignition 1 voltage circuit, sensor side, and the HO2S heater low control circuit, sensor side. Does the resistance measure above or below 2-50 ohms? If yes, go to step  20. If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  16. Test the HO2S heater low control circuit for an open or short to voltage. Did you find and correct the condition? If yes, go to step  22. If no, go to step  18.
  17. Inspect for poor connections at the harness connector of the affected HO2S. Did you find and correct the condition? If yes, go to step  22. If no, go to step  20.
  18. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step  22. If no, go to step  21.
  19. Repair the open in the ignition 1 voltage circuit. After repairs, go to step  22.
  20. Replace the HO2S. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  22.
  21. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  22. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  23. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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