GM Corsica/Beretta 1988-1996 Repair Guide

Engine Coolant Temperature (ECT) Sensor

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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.



Click image to see an enlarged view

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

TESTING



See Figures 2, 3 and 4

Some vehicles are equipped with a 3-terminal ECT sensor. On these vehicles, terminals A and B are the signal terminals and terminal C supplies voltage to the coolant temperature gauge in the dash.

Except 1996 2.2L Engines and 1994-96 3.1L Engines
  1. Visually check the connector, making sure it is connected properly and all of the terminals are straight, tight and free of corrosion.
  2.  
  3. Detach the ECT sensor connector.
  4.  
  5. Carefully remove the cap from the cooling system and place a thermometer in the engine coolant.
  6.  
  7. Measure ECT sensor resistance between terminals A and B with the engine cold and at operating temperature.
  8.  



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Fig. Fig. 2: ECT sensor electrical circuit - 3-terminal sensor shown



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Fig. Fig. 3: ECT sensor electrical circuit - 2-terminal sensor shown

  1. Compare the meter readings with the resistance chart. If the readings aren't within specifications, replace the sensor.
  2.  

1996 2.2L Engines and 1994-96 3.1L Engines

See Figure 4

  1. Remove the ECT sensor from the vehicle.
  2.  
  3. Immerse the tip of the sensor in a container of water.
  4.  
  5. Connect a digital ohmmeter to the two terminals of the sensor.
  6.  
  7. Using a calibrated thermometer, compare the resistance of the sensor to the temperature of the water. Refer to the accompanying resistance value chart.
  8.  



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Fig. Fig. 4: Engine Coolant Temperature (ECT) sensor and Intake Air Temperature (IAT) sensor temperature vs. resistance values

  1. Repeat the test at two other temperature points, heating or cooling the water as necessary.
  2.  
  3. If the sensor does not meet specifications, it must be replaced.
  4.  

REMOVAL & INSTALLATION



See Figure 5

  1. Disconnect the negative battery cable.
  2.  
  3. Relieve the cooling system pressure.
  4.  
  5. If necessary, raise and safely support the vehicle, then drain the cooling system into a suitable container, to a level below the ECT sensor.
  6.  
  7. If raised, lower the vehicle.
  8.  
  9. Detach the electrical connector from the Engine Coolant Temperature (ECT) sensor.
  10.  



Click image to see an enlarged view

Fig. Fig. 5: Unplug the electrical connector (1) from the ECT sensor (2)

  1. Carefully back out the ECT sensor.
  2.  

To install:
  1. Coat the threads of the sensor with a suitable sealer.
  2.  
  3. Install the coolant temperature sensor and tighten as follows:
    1. 2.0L and 2.2L engines: 18.5 ft. lbs. (25 Nm)
    2.  
    3. 2.3L engine: 9.5 ft. lbs. (13 Nm)
    4.  
    5. 2.8L and 3.1L engines: 22 ft. lbs. (30 Nm).
    6.  

  4.  
  5. Attach the sensor electrical connector.
  6.  
  7. Fill the cooling system as required.
  8.  
  9. Connect the negative battery cable.
  10.  
  11. Start the engine and check for leaks.
  12.  

 
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