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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 51 (Engine Control System - Self-Diagnostics - 4.2L) >> Diagnostic Tests >> DTC P0135 & P0141: Ho2S Heater Circuit - Sensors 1 & 2 >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
  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 about one half hour before proceeding with this diagnosis.
  2. Install a scan tool. Turn ON the ignition, with the engine OFF, and immediately record the HO2S signal voltage. Monitor the HO2S signal voltage for 2 minutes. Does the HO2S signal voltage go from bias voltage to more than or less than 300-600 mV? If yes, go to step  8 . If no, go to next step.
  3. Using the scan tool, command the HO2S heater ON. Monitor the HO2S signal voltage for 2 minutes. Does the HO2S signal voltage go from bias voltage to more than or less than 300-600 mV? If yes, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM. If no, go to next step.
  4. Turn OFF the ignition. Disconnect the HO2S connector. 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  11 .
  5. Connect a test lamp between the HO2S heater low control circuit and the HO2S ignition 1 voltage circuit. With a scan tool, command the HO2S heater ON and OFF. Does the test lamp turn ON and OFF with each command? If yes, go to step  9 . If no, go to next step.
  6. Does the test lamp remain illuminated with each command? If yes, go to step  8 . If no, go to next step.
  7. Test the HO2S heater low control circuit for a short to voltage or an open. Did you find and correct the condition? If yes, go to step  14 . If no, go to step  10 .
  8. Test the HO2S heater low control circuit for a short to ground. Did you find and correct the condition? If yes, go to step  14 . If no, go to step  10 .
  9. Inspect for poor connections at the HO2S connector. Did you find and correct the condition? If yes, go to step  14 . If no, go to step  12 .
  10. Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step  14 . If no, go to step  13 .
  11. Repair the HO2S ignition 1 voltage circuit. After repairs, go to step  14 .
  12. Replace the appropriate HO2S. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  14 .
  13. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  14. 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 .
  15. 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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