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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 111 (ENGINE CONTROLS SELF-DIAGNOSTICS - 2.2L)DIAGNOSTIC TESTSDTC P0125: ECT EXCESSIVE TIME TO ENTER CLOSED LOOP FUEL CONTROLDIAGNOSTIC PROCEDURES
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Diagnostic Procedures

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION 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. If cooling system is low on coolant, repair cooling system as necessary. If cooling system is not low on coolant, go to next step.
  3. Turn ignition off. Disconnect ECT sensor. Connect a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the ECT sensor harness connector. Turn ignition on, with engine off. With a scan tool, observe the ECT sensor temperature. Does the scan tool indicate that the ECT sensor temperature is more than 280°F (138°C)? If yes, go to step  7. If no, go to next step.
  4. Turn ignition off. Connect a 3-amp fused jumper wire between the signal circuit of the ECT sensor harness connector and a known-good ground. Turn ignition on, with engine off. With a scan tool, observe the ECT sensor temperature. Does the scan tool indicate that the ECT sensor temperature is more than 280°F (138°C)? If yes, go to next step. If no, go to step  6.
  5. Test the ECT sensor low reference circuit for a high resistance or an open. Repair circuit as necessary. Did you find and correct the condition? If yes, go to step  10. If no, go to DIAGNOSTIC AIDS .
  6. Test the ECT sensor signal circuit for a high resistance or an open. Repair circuit as necessary. Did you find and correct the condition? If yes, go to step  10. If no, go to DIAGNOSTIC AIDS .
  7. Remove the ECT sensor. Suspend the ECT sensor and a thermometer in a pan of water. Place the pan on a burner or hot plate. Test the resistance of the ECT sensor through the specified range of 50-194°F (10-90°C). Does the resistance and temperature closely match the Temperature vs Resistance table? See TEMPERATURE VS RESISTANCE  table. If yes, go to next step. If no, go to step  9.
  8. Reinstall ECT sensor. Diagnose thermostat in engine cooling system.
  9. Replace ECT sensor. After repairs, go to next step.
  10. 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.
  11. Using scan tool, observe stored information. Does scan tool display any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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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.