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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 103 (Engine Controls Self-Diagnostics - 2.2L) >> Diagnostic Tests >> DTC P0140: Ho2S 2 Circuit - Insufficient Activity (SOHC) >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Pontiac Sunfire, 2002 Pontiac Grand Am, 2002 Oldsmobile Alero, and 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
    2. NOTE: Allow the engine to cool for one-half hour before proceeding with this test. This allows HO2S signal voltage to return to bias voltage, about 447 millivolts.
  2. Install scan tool. Turn ignition on, with engine off. Immediately observe the HO2S 2 voltage parameter with a scan tool for 2 minutes. Does the HO2S 2 voltage change from bias voltage to more than or less than the specified of 300-600 millivolts? If yes, go to next step. If no, go to step  5.
  3. Start engine. Allow the engine to reach operating temperature. Operate the engine at 2000 RPM for 30 seconds. While observing the HO2S 2 voltage parameter with a scan tool, quickly cycle the throttle from closed throttle to wide open throttle, 3 times. Did the HO2S 2 voltage change more than 300 millivolts? If yes, go to next step. If no, go to step  5.
  4. 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, go to DIAGNOSTIC AIDS .
  5. Disconnect HO2S 2 connector. Turn ignition on, with engine off. Connect a 3-amp fused jumper wire between the HO2S 2 harness connector high signal circuit and a good ground. Connect a 3-amp fused jumper wire between the HO2S 2 harness connector low signal circuit and a good ground. Observe HO2S 2 voltage parameter with scan tool. Is HO2S 2 voltage less than 200 millivolts? If yes, go to step  9. If no, go to next step.
  6. Remove both jumper wires from the HO2S 2 high signal and low signal circuits. Measure the voltage from the low signal circuit of the HO2S 2 on the engine harness side to a good ground with a DMM. Is the voltage more than 4 volts? If yes, go to next step. If no, go to step  8.
  7. Test the HO2S 2 high signal circuit for an open. Did you find and correct the condition? If yes, go to step  21. If no, go to step  16.
  8. Test the HO2S 2 low signal circuit for an open. Did you find and correct the condition? If yes, go to step  21. If no, go to step  16.
  9. Remove both jumper wires from the HO2S 2 high signal and low signal circuits. Inspect the fuse that provides voltage to the HO2S 2 heater. Is the fuse open? If yes, go to step  12. If no, go to next step.
  10. Turn ignition on, with engine off. Probe the ignition voltage circuit of the HO2S 2 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.
  11. Connect a test light between the ignition voltage circuit of the HO2S 2 on the engine harness side and the heater ground circuit of the HO2S 2 on the engine harness side. Does the test light illuminate? If yes, go to step  15. If no, go to step  18.
  12. Test the ignition voltage circuit of the HO2S 2 for a short to ground. Replace fuse that provides voltage to the HO2S 2 Heater. Did you find and correct a short to ground in the ignition voltage circuit? If yes, go to step  21. If no, go to next step.
  13. Test the HO2S 2 ignition voltage circuit, sensor side, for a short to the HO2S. Did you find the condition? If yes, go to step  19. If no, go to next step.
  14. Measure the resistance between the HO2S 2 ignition voltage circuit, sensor side, and the HO2S 2 heater ground circuit, sensor side with a DMM. Does the resistance measure less than 3 ohms? If yes, go to step  19. If no, go to DIAGNOSTIC AIDS .
  15. Inspect for poor connections at the harness connector of the HO2S 2. Did you find and correct the condition? If yes, go to step  21. If no, go to step  19.
  16. Inspect for poor connections at the PCM. Did you find and correct the condition? If yes, go to step  21. If no, go to step  20.
  17. Repair open in the HO2S 2 ignition voltage circuit. After repairs, go to step  21.
  18. Repair open in the HO2S 2 heater ground circuit. After repairs, go to step  21.
  19. Replace HO2S 2. When complete, go to step  21.
  20. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL, OVERHAUL & INSTALLATION article. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE REPROGRAMMING  under PROGRAMMING. After replacing PCM, go to next step.
  21. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  22. With a scan tool, observe the stored information, Capture Info. 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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