Volvo 240/740/760/780/940/960 1990-1998

Engine Coolant Temperature Sensor

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OPERATION



See Figure 1



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Fig. Fig. 1: Location of the ECT sensor-850/C70/S70/V70 models

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 ECM, which indicates engine coolant temperature. The signal sent to the ECM by the ECT sensor helps the ECM to determine spark advance, EGR flow rate, air/fuel ratio, and engine temperature. The ECT also is used for temperature gauge operation by sending its signal to the instrument cluster.

TESTING



See Figures 2, 3, 4 and 5

  1. Turn the key to the ON position, with the engine OFF .
  2.  
  3. Test the resistance of the sensor across the two terminals of the sensor.
  4.  
  5. Using the chart in this section for a cross reference, check the resistance in relationship to the temperature of the engine.
  6.  
  7. If the sensor is not within specifications, replace it.
  8.  



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Fig. Fig. 2: ECT sensor terminal identification



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Fig. Fig. 3: Unplug the connector from the ECT sensor to test the sensor



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Fig. Fig. 4: Use an ohmmeter and check the sensors resistance based on the temperature of the engine



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Fig. Fig. 5: Engine temperature-to-resistance conversion chart

REMOVAL & INSTALLATION



  1. Disconnect the negative battery cable.
  2.  


CAUTION
Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

  1. Drain and recycle the engine coolant.
  2.  
  3. Remove any components necessary to access the sensor.
  4.  
  5. Remove the connector from the sensor.
  6.  
  7. Using the proper size socket, unscrew the sensor from its mounting location.
  8.  

To install:
  1. Install the sensor in its mounting location and tighten it.
  2.  
  3. Install the connector on the sensor.
  4.  
  5. Install any components removed to access the sensor.
  6.  
  7. Refill and bleed the engine cooling system.
  8.  
  9. Connect the negative battery cable.
  10.  
  11. Inspect for leaks.
  12.  

 
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