GM Astro/Safari 1985-1996 Repair Guide

Engine Coolant Temperature (ECT) Sensor

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OPERATION



See Figure 1



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Fig. Fig. 1: Engine coolant temperature sensors are always mounted in a coolant passage, usually near the thermostat

The Engine Coolant Temperature (ECT) sensor is mounted near the thermostat housing and sends engine temperature information to the ECM. The ECM supplies 5 volts to the coolant temperature sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the ECM monitors a high signal voltage which it interprets as a cold engine. As the sensor warms (internal resistance low), the ECM monitors a low signal voltage which it interprets as warm engine.

TESTING



See Figure 2



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Fig. Fig. 2: Engine coolant temperature sensor resistance chart

  1. Remove the ECT sensor from the vehicle.
  2.  
  3. Immerse the tip of the sensor in 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 engine coolant sensor temperature vs. resistance illustration.
  8.  
  9. Repeat the test at two other temperature points, heating or cooling the water as necessary.
  10.  
  11. If the sensor does not met specification, it must be replaced.
  12.  

REMOVAL & INSTALLATION



See Figures 3 and 4



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Fig. Fig. 3: The ECT is mounted in the intake manifold next to the thermostat housing on the V6 TBI engines



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Fig. Fig. 4: The ECT is mounted in the lower intake manifold in the thermostat housing on the V6 engines

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the cooling system below the level of the sensor and disengage the sensor electrical connection.
  4.  
  5. Remove the coolant sensor.
  6.  

To install:
  1. Install the sensor and the electrical connector.
  2.  
  3. Refill the cooling system and connect the negative battery cable.
  4.  

 
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