GM Cavalier/Sunfire 1995-2000 Repair Guide

Engine Coolant Temperature Sensor

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OPERATION



See Figures 1, 2 and 3



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Fig. Fig. 1: The ECT sensor is located in the water outlet housing, adjacent to where the upper radiator hose connects to the engine



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Fig. Fig. 2: ECT sensor location-2.4L engine



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Fig. Fig. 3: ECT sensor location-1998-00 2.2L engine

The Engine Coolant Temperature (ECT) sensor resistance changes in response to engine coolant temperature. The sensor resistance decreases as the coolant temperature increases, and increases as the coolant temperature decreases. This provides a reference signal to the PCM, which indicates engine coolant temperature. The signal sent to the PCM by the ECT sensor helps the PCM to determine spark advance, EGR flow rate, air/fuel ratio, and engine temperature. The ECT also is used for temperature gauge operation by sending it's signal to the instrument cluster.

The ECT is a two wire sensor, a 5-volt reference signal is sent to the sensor and the signal return is based upon the change in the measured resistance due to temperature.

TESTING



See Figures 4, 5 and 6



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Fig. Fig. 4: Detach the connector on the ECT sensor



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Fig. Fig. 5: Measure the resistance across the ECT terminals on the sensor



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Fig. Fig. 6: ECT sensor resistance value chart

  1. Disconnect the engine wiring harness from the ECT sensor.
  2.  
  3. Connect an ohmmeter between the ECT sensor terminals.
  4.  
  5. With the engine cold and the ignition switch in the OFF position, measure and note the ECT sensor resistance.
  6.  
  7. Connect the engine wiring harness to the sensor.
  8.  
  9. Start the engine and allow the engine to reach normal operating temperature.
  10.  
  11. Once the engine has reached normal operating temperature, turn the engine OFF .
  12.  
  13. Once again, disconnect the engine wiring harness from the ECT sensor.
  14.  
  15. Measure and note the ECT sensor resistance with the engine hot.
  16.  
  17. Compare the cold and hot ECT sensor resistance measurements with the accompanying chart.
  18.  
  19. If readings do not approximate those in the chart, the sensor may be faulty.
  20.  

REMOVAL & INSTALLATION



See Figures 7, 8, 9, 10 and 11



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Fig. Fig. 7: Use a deep well socket to loosen the ECT sensor



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Fig. Fig. 8: Once loose, remove the sensor from the water outlet housing



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Fig. Fig. 9: Use a quality thread sealant and ...



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Fig. Fig. 10: ... apply it to the threads of the ECT sensor



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Fig. Fig. 11: Tighten the sensor using a torque wrench, or the housing may crack if you over-tighten it

  1. Disconnect the negative battery cable.
  2.  
  3. Drain and recycle the engine coolant.
  4.  
  5. Remove the air cleaner outlet tube.
  6.  
  7. Unplug the ECT electrical connection.
  8.  
  9. Using an appropriate tool, loosen the ECT sensor and remove it from the engine.
  10.  

To install:
  1. Use a suitable thread sealant and apply it to the threads of the ECT sensor.
  2.  
  3. Install the ECT sensor and tighten it to 18 ft. lbs. (25 Nm).
  4.  
  5. Attach the ECT connector.
  6.  
  7. Refill and bleed the cooling system.
  8.  
  9. Connect the negative battery cable.
  10.  

 
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