Subaru Coupes/Sedans/Wagons 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 sensor in the intake manifold-Impreza

The ECT sensor is installed on the coolant passage wall of the intake manifold. The thermistor inside changes resistance with to coolant temperature changes. The ECT sensor sends the coolant temperature signal to the ECU, which determines the fuel quantity to be injected and the ignition timing.

TESTING



See Figure 2

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Fig. Fig. 2: Testing the coolant temperature sensor

  1. Remove the temperature sensor from the thermostat housing.
  2.  
  3. Place the sensor in water of various temperatures and measure the resistance between the terminals with an ohmmeter.
  4.  
  5. For all models, the resistance should be 3.0 kilo-ohms at 68°F (20°C).
  6.  
  7. At 122°F (50°C), the resistance should be 0.7-1.0 kilo-ohms,
  8.  
  9. At 176°F (80°C), the resistance should be 0.3-0.4 kilo-ohms.
  10.  
  11. If the resistance is not within specification, replace the ECT sensor.
  12.  

REMOVAL & INSTALLATION



  1. Disconnect the negative battery cable.
  2.  
  3. Drain the engine coolant below the level of the intake manifold.
  4.  
  5. Locate the temperature sensor at the water housing on the intake manifold and remove the ECT sensor with a suitable wrench.
  6.  

To install:
  1. Coat the ECT sensor threads with sealant and install. Tighten the sensor securely.
  2.  
  3. Connect the electrical connector.
  4.  
  5. Fill the engine with coolant.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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