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Home › Buick › 2003 › Century Base › Repair and Diagnosis › Engine Performance › System › Engine Controls Self-Diagnostics - 3.1L Engine › Diagnostic Tests › DTC P0125: Engine Coolant Temperature Insufficient For Closed Loop Fuel Control › Diagnostic Procedure

Diagnostic Procedure

  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: The cooling fans are commanded ON when certain engine coolant temperature DTCs are set.
  2. Is the cooling system coolant low? If yes, repair cause of coolant loss and refill system. If no, go to next step.
  3. Check and verify the proper operation of the thermostat. For thermostat specifications, see appropriate SPECIFICATIONS & DRIVE BELT ROUTING article under COOLING SYSTEM (MECHANICAL). Did you find and correct the condition? If yes, go to step  14. If no, go to next step.
  4. Disconnect the ECT sensor harness connector. Check for corrosion on the ECT sensor terminals, improper or corroded terminals at the ECT harness connector and loose terminals in the ECT harness connector. Did you find and correct the condition? If yes, go to step  14. If no, go to next step.
  5. Measure the voltage from the ECT sensor signal circuit to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to next step. If no, go to step  8.
  6. Measure the voltage from the ECT sensor signal circuit to the ECT sensor low reference circuit using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to step  9. If no, go to next step.
  7. Check the ECT sensor low reference circuit for high resistance. Did you find and correct the condition? If yes, go to step  14. If no, go to step  11.
  8. Test the ECT sensor signal circuit for high resistance. Did you find and correct the condition? If yes, go to step  14. If no, go to step  11.
  9. Turn ignition switch to OFF position. Remove the ECT sensor. Place the sensor on a work surface away from any heat source. Allow the sensor to reach the ambient air temperature for 30-60 minutes. Observe and record the ambient air temperature of the vehicle environment using an accurate thermometer. Measure the resistance of the ECT sensor and record the value. Compare the resistance measurement of the ECT sensor to the ambient air temperature. See TEMPERATURE VS. RESISTANCE  table. Is the resistance measurement of the ECT sensor within the specified range? If yes, go to step  10. If no, go to step  12.
  10. Install the ECT sensor. After installation of ECT sensor is complete, go to INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  11. Check for an intermittent and for a poor connection at the PCM. Did you find and correct the condition? If yes, go to step  14. If no, go to step  13.
  12. Reinstall ECT sensor. After installation, go to step  14.
  13. Replace ECT sensor. After repair, go to next step.
  14. 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.
  15. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay at this time.
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