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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 P0116: ECT Sensor Circuit Performance >> Diagnostic Procedure
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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 (ECT) DTCs are set.
  2. Check the cooling system coolant level. Is the cooling system coolant low? If yes, repair cause of coolant loss and refill system.
  3. Observe and record the ambient air temperature of the vehicle environment using an accurate thermometer. After completing the action, go to next step.
    4. NOTE: The vehicle needs to have been OFF for at least 8 hours for the ECT and the Intake Air Temperature (IAT) to be at ambient temperature. The vehicle should not have changed environments during this time.
  4. Has the engine been OFF for 8 hours? If yes, go to step  7. If no, go to next step.
  5. Remove the IAT sensor. Remove the ECT sensor. Place the sensors on a work surface away from any heat source. Allow the sensors to reach the ambient air temperature for 30-60 minutes. After the sensors at the ambient temperature, go to next step.
  6. Connect the IAT sensor to the IAT harness connector, but Do NOT install it. Insulate the sensor from any engine heat source. Connect the ECT sensor to the ECT harness connector, but Do NOT install it. Insulate the sensor from any engine heat source. After the sensors connected, go to next step.
  7. Turn ignition switch to RUN position. Take a snapshot of the ENGINE DATA LIST using a scan tool. Review the snapshot data that was taken. Observe the ECT Sensor parameter. Observe the IAT Sensor parameter. Is the difference between the ECT Sensor parameter and the IAT Sensor parameter more than 27°F (15°C)? If yes, go to next step. If no, go to INTERMITTENTS in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.
  8. Observe the recorded IAT Sensor parameter. Is the difference between the IAT Sensor parameter and the ambient air temperature less than 14°F (8°C)? If yes, go to next step. If no, go to step  12.
  9. Observe the recorded ECT Sensor parameter. Is the difference between the ECT Sensor parameter and the ambient air temperature less than 14°F (8°C)? If yes, go to INTERMITTENTS in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to step  12.
  10. Disconnect the IAT sensor harness connector. Test for an intermittent and for a poor connection at the IAT sensor. Did you find and correct the condition? If yes, go to step  25. If no, go to next step.
  11. At the sensor, measure the resistance between the IAT signal and the IAT low reference terminals using a DMM and record the value. Observe the recorded ambient air temperature. Compare the resistance measurement of the IAT sensor to the ambient air temperature using the Temperature vs. Resistance table. See TEMPERATURE VS. RESISTANCE  table. Is the resistance measurement of the IAT sensor within the specified range? If yes, go to step  14. If no, go to step  22.
  12. Disconnect the ECT sensor harness connector. Check for the following conditions:
    • An ECT sensor leaking engine coolant internally through the sensor.
    • Corrosion on the ECT sensor terminals.
    • Corrosion on the ECT harness connector terminals.

    Did you find and correct the condition? If yes, go to step  25. If no, go to next step.

  13. At the sensor, measure the resistance between the ECT signal and the ECT low reference terminals using a DMM and record the value. Observe the recorded ambient air temperature. Compare the resistance measurement of the ECT sensor to the ambient air temperature using the Temperature vs. Resistance table. See TEMPERATURE VS. RESISTANCE  table. Is the resistance measurement of the ECT sensor within the specified range? If yes, go to step  15. If no, go to step  23.
  14. Measure the voltage from the IAT signal circuit to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to INTERMITTENTS in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to step  17.
  15. Measure the voltage from the ECT signal circuit to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to INTERMITTENTS in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to step  19.
    16. NOTE: All electrical components and accessories must be turned OFF. Performing this step will disable the diagnostic for 8 hours.
  16. Turn ignition switch to OFF position for 90 seconds to allow the control modules to power down. Measure the resistance from the IAT sensor low reference circuit to a good ground using a DMM. Is the resistance less than 5 ohms? If yes, go to INTERMITTENTS in TROUBLE SHOOTING - 3.1L CENTURY, GRAND PRIX & MALIBU article. If no, go to step  18.
  17. Test the IAT signal circuit for a high resistance. Did you find and correct the condition? If yes, go to step  25. If no, go to step  20.
  18. Test the ECT signal circuit for a high resistance short to ground. Did you find and correct the condition? If yes, go to step  25. If no, go to step  20.
  19. Test the ECT signal circuit for a high resistance short to ground. Did you find and correct the condition? If yes, go to step  25. If no, go to step  21.
  20. Test for an intermittent and for a poor connection at the Powertrain Control Module (PCM). Did you find and correct the condition? If yes, go to step  25. If no, go to step  24.
  21. Test for shorted terminals and poor connections at the PCM. Did you find and correct the condition? If yes, go to step  25. If no, go to step  24.
  22. Replace the IAT sensor. After repair, go to step  25.
  23. Replace the IAT sensor. After repair, go to step  25.
  24. Replace PCM. See appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repair, go to next step.
  25. Reassemble the vehicle as necessary. After repair, go to next step.
    26. NOTE: This DTC will not run without the ignition being OFF for at least 8 hours.
  26. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 8 hours. 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.
  27. Using the scan tool, observe the stored information in CAPTURE INFO. Are there any DTCs that have not been diagnosed? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay at this time.
TEMPERATURE VS. RESISTANCE

°F (°C) Ohms
302 (150) 47
284 (140) 60
266 (130) 77
248 (120) 100
230 (110) 132
212 (100) 177
194 (90) 241
176 (80) 332
158 (70) 467
140 (60) 667
122 (50) 973
113 (45) 1188
104 (40) 1459
95 (35) 1802
86 (30) 2238
77 (25) 2796
68 (20) 3520
59 (15) 4450
50 (10) 5670
41 (5) 7280
32 (0) 9420
23 (-5) 12,300
14 (-10) 16,180
5 (-15) 21,450
-4 (-20) 28,680
-22 (-30) 52,700
-40 (-40) 100,700
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