GM Cadillac Deville_Fleetwood_ELD_Seville 1990-1998

Coolant Temperature Sensor

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OPERATION



The engine coolant temperature sensor is a thermistor (a resistor which changes value based on temperature) mounted in the engine coolant stream. Low coolant temperature produces a high resistance (100,000 ohms{100K ohms} at -40°C/-40°F) While high temperature causes low resistance (70 ohms at 130°C/266°F).

The PCM supplies a 5 volt signal to the engine 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. By measuring the voltage, the PCM calculates the engine coolant temperature. The scan tool displays engine coolant temperature in degrees. After engine start-up, the temperature should rise steadily to about 90°C (194°F) then stabilize when ht thermostat open. If the engine has not been run for several hours (overnight), the engine coolant temperature and intake air temperature displays should be close to each other.

Engine coolant temperature affects most systems the PCM controls.

TESTING



  1. Detach the electrical connector.
  2.  
  3. Attach an ohmmeter to the sensor terminals and then measure the resistance and compare with the accompanying chart on a cold engine. Measure the coolant temperature in the radiator or overflow bottle.
    1. Compare the resistance and temperature on the chart.
    2.  

  4.  
  5. Tape an automotive thermometer tightly to the upper radiator hose. Start and run the engine to normal operating temperature, comparing the temperature on the thermometer to the resistance reading on the ohmmeter. The readings should coincide with the chart.
  6.  
  7. If the sensor is not in specification, replace it.
  8.  



Click image to see an enlarged view

Fig. Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) Sensor Resistance Values vs. Temperature Readings

Sensor Removed From Vehicle
  1. Remove the ECT from the vehicle.
  2.  
  3. Immerse the tip of the sensor in a container of icy water (0°C/32°F), as measured with a calibrated thermometer.
  4.  
  5. Attach an Ohmmeter to the sensor connector. The Ohms value should read approximately 9400 to 9500 Ohms.
  6.  
  7. Using the thermometer readings, compare the resistance of the sensor to the temperature of the water.
  8.  
  9. Repeat the test at two other temperature readings, heating the water as necessary.
  10.  
  11. Refer to the resistance value chart; if the sensor is not within specification, replace it.
  12.  

REMOVAL & INSTALLATION




NOTE
Use care when handling the ECT sensor. Damage to the coolant sensor will affect the operation of the fuel control system.


NOTE
The engine coolant temperature sensor is located on the intake manifold water jacket or near the thermostat housing. On the 4.6L engine, the coolant temperature sensor is located on the rear cylinder head, at the cruise control servo bracket. It is necessary to drain coolant from the cooling system to a level below the sensor, prior to sensor removal.

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the coolant level below the height of the ECT and recycle the engine coolant.
  4.  
  5. Detach the electrical connector at the sensor.
  6.  
  7. Remove any obstruction to access the ECT.
    1. On the Catera, this would include removing the intake plenum and the intake bridge.
    2.  

  8.  
  9. Using a deep well socket, remove the sensor.
  10.  

To install:

  1. Coat the threads of the new sensor and install it in the engine. Tighten to 15 ft. lbs. (20 Nm).
  2.  
  3. Install the electrical connector.
  4.  
  5. Refill the system with coolant.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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