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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 102 (Engine Controls - Self-Diagnostics - 3.5L) >> Diagnostic Tests >> DTC P0140: Ho2S Circuit Insufficient Activity (Bank 1; Sensor 2) >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Intrigue and 2002 Oldsmobile Aurora. 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, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Using scan tool, clear DTCs. Reset fuel trim values. Start engine. Ensure engine is at normal operating temperature. Using scan tool, observe HO2S bank 1 sensor 2 voltage. If scan tool indicates voltage is fixed within 351-551 millivolts, go to step  4. If scan tool indicates voltage is not fixed within 351-551 millivolts, go to next step.
  3. Condition that set this DTC is not present. This DTC may have been set by one of the following conditions:
    • HO2S connector water intrusion.
    • An intermittently open HO2S high signal circuit.
    • An intermittently open HO2S low reference circuit.
    • A HO2S low reference circuit with high resistance to ground.
    • PCM ground circuits with high resistance to ground.
    • An inoperative HO2S heater.
    • Poor HO2S or PCM connector terminal contact.
    • An exhaust system leak, typically within 12" upstream of HO2S.

    Check conditions listed for faults. If any problems are found, repair as necessary. After repairs, go to step  17. If no problems are found, see DIAGNOSTIC AIDS .

  4. Turn ignition off. Disconnect HO2S connector for the sensor that applies to this DTC. Jumper HO2S low reference circuit to a known-good ground. Jumper HO2S high signal circuit to a known-good ground. Turn ignition on, with engine off. Use scan tool to monitor HO2S voltage for the sensor that applies to this DTC. Is HO2S voltage less than 20 millivolts? If yes, go to step  7. If no, go to next step.
  5. Turn OFF the ignition. Remove jumpers from the HO2S terminals. Disconnect the PCM connector containing the HO2S high and low circuits. Use a Digital Multimeter (DMM) in order to first measure the continuity of HO2S high signal circuit. Then measure continuity of HO2S low reference circuits between PCM connector terminal and engine harness side of HO2S connector terminal. Is individual resistance of both circuits less than 5 ohms? If yes, go to next step. If no, go to step  9.
  6. Check for poor connections at PCM connectors. Repair connectors as necessary. After repairs, go to step  17. If connectors are okay, go to next step.
  7. Remove the jumpers from HO2S terminals. Connect a test light between the HO2S ignition 1 voltage circuit and engine harness side of heater ground circuit terminals. Start engine. Does test light illuminate? If yes, go to next step. If no, go to step  10.
  8. Turn ignition off. Reconnect HO2S connector. Disconnect PCM connector containing the HO2S low reference circuit and PCM connector containing the PCM ground circuits. Use DMM to measure the resistance between HO2S low reference circuit terminal and one of the PCM ground circuit terminals. Is resistance measured less than 500 ohms? If yes, go to step  12. If no, go to step  11.
  9. Repair circuit that measured high resistance. After repairs, go to step  17.
  10. Repair the HO2S ignition 1 voltage circuit or HO2S heater low control circuit. After repairs, go to step  17.
  11. Repair high resistance between HO2S low reference circuit and PCM ground circuit. Possible causes include the following:
    • Poor HO2S connector terminal contact.
    • Faulty HO2S.
    • Poor PCM ground connection.
    • High PCM ground circuit resistance.
    • Ungrounded exhaust system.

    Repair as necessary. After repairs, go to step  17.

  12. Check for exhaust leaks upstream of HO2S. Leak may be very small and within 12" of HO2S. Repair exhaust system as necessary. After repairs, go to step  17. If exhaust system is okay, go to next step.
  13. Allow engine to cool to ambient temperature. Measure resistance between the HO2S low reference circuit terminal and a PCM ground circuit terminal. Is resistance is less than 500 ohms? If yes, go to step  15. If no, go to next step.
  14. Remove HO2S. Clean HO2S threads. Apply anti-seize to HO2S threads and reinstall sensor. Tighten sensor to 30 ft. lbs. (41 N.m). Measure resistance between HO2S low reference circuit terminals and a PCM ground circuit terminal. Is resistance less than 500 ohms? If yes, go to step  17. If no, go to next step.
  15. Replace HO2S. After repairs, go to step  17.
  16. Replace PCM. Program replacement PCM. See PROGRAMMING . After repairs, go to next step.
  17. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within conditions for running the DTC. See CONDITIONS FOR RUNNING DTC . If DTC runs and passes, go to next step. If DTC resets, go to step  2.
  18. Using scan tool, check for any other DTCs that are set. If no other DTCs are set, system is okay. If any other DTCs are set, repair DTCs as necessary. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
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