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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 378 (Engine Controls Self-Diagnostics - 3.1L Engine) >> Diagnostic Tests >> DTC P0140: Ho2S 2 Circuit - Insufficient Activity >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2003 Pontiac Grand Prix, 2003 Chevrolet Malibu, and 2003 Buick Century. 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. Start the engine. Allow the engine to idle at operating temperature. Clear the DTC and record the Freeze/Frame Failure Records. Observe the Heated Oxygen Sensor (HO2S) 2 voltage parameter using a scan tool. Vary the engine speed from idle to 3000 RPM several times within 5 seconds. Does the HO2S 2 voltage fluctuate above and below 375-475 mV? If yes, go to next step. If no, go to step  4.
  3. Observe the Freeze Frame/Failure Records for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See CONDITIONS FOR RUNNING TEST . 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 INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  4. Turn ignition switch to RUN position. Disconnect the HO2S 2 harness connector. Connect a 3-amp fused jumper wire between the HO2S 2 low signal circuit of the engine harness and a good ground. Connect a 3-amp fused jumper wire between the HO2S 2 high signal circuit of the engine harness and a good ground. Turn ignition switch to RUN position, engine OFF. Observe the HO2S 2 voltage parameter using a scan tool. Is the HO2S 2 voltage less than 25 mV? If yes, go to step  7. If no, go to next step.
  5. Turn ignition switch to OFF position. Disconnect the Powertrain Control Module (PCM). Measure the resistance of the HO2S 2 high signal circuit. Measure the resistance of the HO2S 2 low signal circuit. Is the resistance 0-5 ohms? If yes, go to step  9. If no, go to next step.
  6. Repair the signal circuit that has an open or high resistance. After repair, go to step  12.
  7. Check for the following that may affect the HO2S operation:
    • HO2S for contamination.
    • Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring.
    • The HO2S must have a clean air reference to function properly. This clean air reference is obtained by way of the HO2S wires. Obstruction of the air reference and degraded HO2S performance could result from any attempt to repair the above conditions.
    • Exhaust system leaks or restrictions. See EXHAUST SYSTEM CHECK in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
    • Evaporative Emissions (EVAP) system malfunction. EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
    • The fuel pressure. Incorrect fuel pressure can affect HO2S operation. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 3.1L CENTURY, GRAND PRIX & MALIBU article.

    Did you find and correct the condition? If yes, go to step  12. If no, go to next step.

  8. Test for an intermittent and for a poor connection at the HO2S 2 harness connector. Did you find and correct the condition? If yes, go to step  12. If no, go to step  10.
  9. Test for an intermittent and for a poor connection at the PCM harness connector. Did you find and correct the condition? If yes, go to step  12. If no, go to next step  11.
  10. Replace the HO2S 2. After repair, go to step  12.
  11. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After replacing PCM, go to next step.
  12. Using scan tool, clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running Test. See CONDITIONS FOR RUNNING TEST . 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.
  13. Using the scan tool, observe the stored information in 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 at this time.
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