GM Caprice 1990-1993 Repair Guide

Coolant Temperature Sensor (CTS)

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See Figure 1



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Fig. Fig. 1: Coolant temperature sensor (CTS)

OPERATION



Most engine functions are effected 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 ECM is supplied by the coolant temperature 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 (100,000 ohms at -40°F/-40°C) and high coolant temperature produces low resistance (70 ohms at 266°F/130°C). The ECM supplies a signal of 5 volts to the coolant temperature sensor through a resistor in the ECM and measures the voltage. The voltage will be high when the engine is cold and low when the engine is hot.

TESTING



  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the coolant temperature sensor wire connector.
  4.  
  5. Connect a volt/ohmmeter to the terminals of the coolant temperature sensor and verify the reading is within range on the appropriate diagnostic CODE chart.
  6.  

REMOVAL & INSTALLATION



  1. Disconnect the negative battery cable.
  2.  
  3. Drain the cooling system into a clean container for reuse.
  4.  
  5. Disconnect the electrical connector from the coolant temperature sensor.
  6.  
  7. Remove the coolant temperature sensor.
  8.  

To install:
  1. Install the coolant temperature sensor.
  2.  
  3. Connect the electrical connector.
  4.  
  5. Fill the cooling system.
  6.  
  7. Connect the negative battery cable.
  8.  
  9. Start the engine and check for leaks.
  10.  

 
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