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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 370 (Engine Control System - Self-Diagnostics - 4.2L) >> Diagnostic Tests >> DTC P0135 Or P0141: Ho2S Heater Circuit (Bank 1; Sensor 1 Or 2) >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Oldsmobile Bravada, 2003 GMC Envoy XL, 2003 GMC Envoy, and 2003 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. Turn ignition on, with engine off. Command the affected HO2S heater ON with a scan tool. Wait 15 seconds to allow the HO2S heater current to stabilize. Observe the affected HO2S heater current parameter with a scan tool. Is the HO2S heater current parameter within 0.22-1.56 amps? If yes, go to next step. If no, go to step  4.
  3. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions For Running the DTC. See CONDITIONS FOR RUNNING DTC . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
  4. Inspect the O2 fuse. Is O2 fuse open? If yes, go to next step. If no, go to step  6.
  5. Test the ignition 1 voltage circuit for a short to ground. Did you find and correct the condition? If yes, go to step  20. If no, go to step  8.
  6. Disconnect the affected HO2S. Turn ignition on, with engine off. Probe the ignition 1 voltage circuit of the HO2S harness connector on the engine harness side with a test light that is connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step  17.
  7. Connect a test light between the ignition 1 voltage circuit of the HO2S harness connector on the engine harness side and the HO2S heater low control circuit of the HO2S harness connector on the engine harness side. Command the affected HO2S heater ON and OFF with a scan tool. Does the test light turn ON and OFF with each command? If yes, go to step  9. If no, go to step  10.
    8. NOTE: Perform the following test on all HO2S which are supplied voltage by the suspect circuit.
  8. Test the ignition 1 voltage circuit on the sensor side of the HO2S connector for a short to ground. Is any sensor shorted to ground? If yes, go to step  18. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
  9. Measure the resistance of the following circuits with a DVOM: HO2S heater low control circuit, and ignition 1 voltage circuit. Is the resistance of either circuit more than 3 ohms? If yes, go to step  16. If no, go to step  14.
  10. Does the test light remain illuminated with each command? If yes, go to next step. If no, go to step  12.
  11. Test the HO2S heater low control circuit for a short to ground. Did you find and correct the condition? If yes, go to step  20. If no, go to step  15.
  12. Test the HO2S heater low control circuit for a short to voltage. Did you find and correct the condition? If yes, go to step  20. If no, go to next step.
  13. Test the HO2S heater low control circuit for an open. Did you find and correct the condition? If yes, go to step  20. If no, go to step  15.
  14. Test for an intermittent and for a poor connection at the HO2S. Did you find and correct the condition? If yes, go to step  20. If no, go to step  18.
  15. Test for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step  20. If no, go to step  19.
  16. Repair circuit with high resistance. After repairs, go to step  20.
  17. Repair open in the ignition 1 voltage circuit. After repairs, go to step  20.
  18. Replace HO2S. See REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. After replacing sensor, go to step  20.
  19. Replace PCM. See REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  20. Were you sent to this diagnostic from DTC P0134? If yes, go to step  18 in DTC P0134. If no, go to next step.
  21. Were you sent to this diagnostic from DTC P0140? If yes, go to step  18 in DTC P0140. If no, go to next step.
  22. Replace the O2 fuse, if necessary. Clear the DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running the DTC. See CONDITIONS FOR RUNNING DTC . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step  2. If no, go to next step.
  23. Observe the stored information, Capture Info with scan tool. Does 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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