Honda - Accord Prelude 1996 2000

Engine Coolant Temperature Sensor

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OPERATION





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Fig. The Engine Coolant Temperature (ECT) sensor is a thermistor; a sensor whose resistance changes is response to coolant temperature

The Engine Coolant Temperature (ECT) sensor is a thermistor, which means it's 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 input signal is used by the ECM/PCM help determine the correct air-to-fuel ratio for the engine's operating temperature. The ECM/PCM controls the fuel mixture by controlling how long the electrically triggered fuel injectors stay open. If the ECT sensor is unplugged, the ECM/PCM senses a very high resistance, and the engine may start when cold, however as the engine's temperature increases, a rich running condition will cause the engine to loose power and stall.

TESTING





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Fig. ECT sensor temperature vs. resistance chart

  1. Disconnect the engine wiring harness from the ECT sensor.
  2.  
  3. Connect an ohmmeter between the two ECT sensor terminals.
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  5. With the engine cold and the ignition switch in the OFF position, measure and note the ECT sensor resistance.
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  7. Connect the engine wiring harness to the sensor.
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  9. Start the engine and allow the engine to reach normal operating temperature.
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  11. Once the engine has reached normal operating temperature, turn the engine OFF .
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  13. Again, disconnect the engine wiring harness from the ECT sensor.
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  15. Measure and note the ECT sensor resistance with the engine hot.
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  17. The ECT sensor should have 5,000 ohms resistance when the engine coolant temperature is cold. The ECT sensor resistance should decrease as the engine temperature increases. At operating temperature the ECT sensor resistance should be 100-400 ohms.
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  19. If readings are not close, the sensor may be faulty.
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REMOVAL & INSTALLATION





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Fig. Unplug the ECT sensor electrical connector . . .



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Fig. . . . then remove the ECT sensor from the thermostat housing

  1. Disconnect the negative battery cable.
  2.  
  3. Drain and recycle the engine coolant, to a level below the sensor.
  4.  


CAUTION
Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. In addition, 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. Detach the ECT sensor electrical connector.
  2.  
  3. Unthread and remove the ECT sensor from the thermostat housing
  4.  

To install:

  1. Coat the sensor threads with a suitable Teflon® sealant.
  2.  
  3. Thread the sensor into position and tighten securely.
  4.  
  5. Attach the ECT sensor connector.
  6.  
  7. Connect the negative battery cable.
  8.  
  9. Refill the engine cooling system.
  10.  
  11. Start the engine and check for coolant leaks.
  12.  
  13. Bleed the cooling system as necessary.
  14.  

 
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