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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G2500, VAN CARGO, 6.6 6REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 28 (ENGINE CONTROL SYSTEM - SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P0125: ECT EXCESSIVE TIME TO ENTER CLOSED LOOPDIAGNOSTIC PROCEDURES
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6

Diagnostic Procedures

2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6SECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2003 Pontiac Vibe. 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, perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Start engine. Run engine until it reaches normal operating temperature. Select HO2S 1 parameter on scan tool. Snap throttle. Observe HO2S 1 parameter. Does HO2S 1 voltage vary within 200-900 mV? If yes, go to next step. If no, go to step  4.
  3. Use scan tool to clear DTCs. Place vehicle into CHECK MODE, using scan tool. See SERVICE BAY TESTS . Operate vehicle within freeze frame conditions as specified. Does DTC P0125 set? If yes, go to next step. If no, go to DIAGNOSTIC AIDS .
  4. Disconnect HO2S 1 harness connector located behind front floor console. Turn ignition switch to RUN position, engine OFF. Select DMM to measure DC millivolts. Place positive lead of DMM on positive battery voltage, and negative lead on HO2S 1 input circuit terminal on engine harness side. Observe HO2S 1 voltage on scan tool. Is voltage more than 1155 mV? If yes, go to next step. If no, go to step  6.
  5. Connect a test light to battery voltage. Probe HO2S 1 ground circuit terminal on engine harness side. Does test light illuminate? If yes, go to step  8. If no, go to step  7.
  6. Check for an open or short in HO2S 1 input circuit between HO2S 1 and PCM connector. Repair as necessary. Did you find and repair a condition? If yes, go to step  11. If no, go to step  10.
  7. Repair open in HO2S 1 ground circuit between HO2S 1 and ground point G104. After repair, go to step  11.
  8. Before replacing oxygen sensor, check for the following conditions:
    • Lean or rich fueling condition.
    • Vacuum leaks.
    • Exhaust leaks.
    • An intermittent or a poor electrical connection at HO2S.
    • Refer to DIAGNOSTIC AIDS  for a complete list of items to check and test.
    Repair any condition found as necessary. Did you find and repair a condition? If yes, go to step  11. If no, go to next step.
  9. Replace HO2S 1. After replacing sensor, go to step  11.
  10. Replace PCM. After replacing PCM, go to next step.
  11. Use scan tool to clear DTCs. Turn ignition OFF for 30 seconds. Start engine. Operate vehicle within Conditions for Running DTC as specified in supporting text. See CONDITIONS FOR RUNNING DTC . Does DTC run and pass? If yes, go to next step. If no, go to step  2.
  12. Using scan tool, observe the stored information, CAPTURE INFO. Does scan tool display any DTCs that you have not diagnosed? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay at this time.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.