GM Bonneville/Eighty Eight/LeSabre 1986-1999

Coolant Temperature Sensor

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OPERATION



See Figure 1

Most engine functions are affected by the coolant temperature. Determining whether the engine is hot or cold is largely dependent on the temperature of the coolant. An accurate temperature signal to the PCM is supplied by the coolant temperature sensor or Engine Coolant Temperature (ECT) sensor. The coolant temperature sensor is a thermistor mounted in the engine coolant stream. A thermistor is an electrical device that varies its resistance in relation to changes in temperature. Low coolant temperature produces a high resistance, and high coolant temperature produces low resistance. The PCM supplies a signal of 5 volts to the coolant temperature sensor through a resistor in the PCM and measures the voltage. The voltage will be high when the engine is cold and low when the engine is hot.



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Fig. Fig. 1: Engine Coolant Temperature (ECT) sensor and connector

TESTING



Sensor in Vehicle

See Figures 2, 3, 4, 5 and 6

  1. Unfasten the retaining bolts, then remove the bracket.
  2.  



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Fig. Fig. 2: Unfasten the retainers, then remove the throttle bracket for more access to the sensor

  1. Use a long screwdriver or prytool to lift the ECT sensor locking tab and detach the connector.
  2.  



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Fig. Fig. 3: Use a long screwdriver to carefully lift the sensor locking tab, then unplug the connector

  1. Attach an ohmmeter to the sensor terminals, then measure the resistance and compare with the accompanying chart.
  2.  



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Fig. Fig. 4: Use needlenose pliers to attach an ohmmeter to the sensor terminals, then measure resistance (tested at 80°F)



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Fig. Fig. 5: Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) sensor temperature vs. resistance values



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Fig. Fig. 6: Engine Coolant Temperature (ECT) and Throttle Position (TP) sensor circuits

Sensor Removed From Vehicle

See Figure 7

  1. Remove the ECT sensor from the vehicle.
  2.  
  3. Immerse the tip of the sensor in a container of water.
  4.  



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Fig. Fig. 7: Submerge the end of the temperature sensor in cold or hot water and check resistance

  1. Connect a digital ohmmeter to the two terminal of the sensor.
  2.  
  3. Using a calibrated thermometer, compare the resistance of the sensor to the temperature of the water. Refer to the accompanying resistance value chart.
  4.  
  5. Repeat the test at two other temperature points, heating or cooling the water as necessary.
  6.  
  7. If the sensor does not meet specifications, it must be replaced.
  8.  

REMOVAL & INSTALLATION



See Figures 8, 9, 10 and 11

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the radiator into a suitable container, to a level below the sensor.
  4.  
  5. For 1987-91 vehicles, perform the following:
    1. Properly relieve the fuel system pressure, as outlined in Fuel System .
    2.  
    3. Unfasten the 10mm bolt and bracket holding the fuel line to the throttle cable bracket.
    4.  
    5. Loosen the fuel supply and return lines from the fuel rail and carefully move aside.
    6.  
    7. Fabricate a loop of wire or use a long prytool to slip under the locking tab of the electrical connector and gently pull on the tab to disengage it.
    8.  

  6.  
  7. For 1992-99 vehicles, perform the following:
    1. Remove the air induction tube or rear air intake duct, as applicable.
    2.  
    3. Detach the sensor electrical connector.
    4.  

  8.  
  9. Using a 19mm deep well socket and extension, remove the sensor.
  10.  



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Fig. Fig. 8: Location of the ECT sensor - 3.8L (VIN L) engine shown



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Fig. Fig. 9: Exploded view of the ECT sensor mounting - 3.8L (VIN 1) engine



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Fig. Fig. 10: ECT sensor location - 3.8L (VIN 1) engine



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Fig. Fig. 11: Insert the ECT sensor into its mounting hole - 1996-99 vehicles

To install:
  1. Coat the ECT sensor threads with a suitable sealant.
  2.  
  3. Install the sensor and tighten to 22 ft. lbs. (30 Nm).
  4.  
  5. For 1992-99 vehicles perform the following:
    1. Attach the sensor electrical connector.
    2.  
    3. For VIN 1 and L engines, install the air induction tube.
    4.  

  6.  
  7. For 1987-91 vehicles, perform the following:
    1. Attach the electrical connector.
    2.  
    3. Connect the fuel supply and return lines.
    4.  
    5. Install the fuel line bracket.
    6.  

  8.  
  9. Connect the negative battery cable, then refill the cooling system.
  10.  

 
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