Quest 1995-1996

Engine Coolant Temperature Sensor

Print

Location



Specific to:

Mercury Villager 1993-2000

Nissan Quest 1993-2000

The coolant temperature sending unit is located in the intake manifold coolant outlet, where the upper radiator hose is connected to the engine.

Operation



Specific to:

Mercury Villager 1993-2000

Nissan Quest 1993-2000

The Engine Coolant Temperature (ECT) sensor resistance changes in response to the engine coolant temperature. The sensor resistance decreases as the coolant temperature increases. This provides a reference signal to the PCM, which indicates engine coolant temperature. The signal sent to the PCM by the ECT sensor helps the PCM to determine spark advance, EGR flow rate, air/fuel ratio, and engine temperature. A 5 volt reference signal is sent to the sensor and the signal return is based upon the change in the sensor resistance due to temperature.

Removal & Installation



Specific to:

Mercury Villager 1993-2000

Nissan Quest 1993-2000

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the radiator and recycle the engine coolant.
  4.  
  5. Disconnect the ECT sensor electrical connector.
  6.  
  7. Remove the ECT sensor from the intake manifold coolant outlet.
  8.  

To install:

  1. Coat the ECT sensor threads with Teflon® tape or electrically conductive sealer.
  2.  
  3. Install the sensor and tighten it to 11-14 ft. lbs. (15-20 Nm).
  4.  
  5. Connect the sensor electrical connector.
  6.  
  7. Fill the engine with coolant.
  8.  
  9. Start the engine, allow it to reach operating temperature, bleed the cooling system, and check for leaks.
  10.  

Testing



Specific to:

Mercury Villager 1993-2000

Nissan Quest 1993-2000

  1. Let the engine cool completely before beginning the test.
  2.  
  3. Disconnect the sending unit wire.
  4.  
  5. Connect ohmmeter leads to the sending unit terminal and the negative battery terminal.
  6.  
  7. Start the engine and observe the ohmmeter. The resistance should gradually decrease as the engine warms up. When the engine has reached normal operating temperature, the resistance should be approximately 60-72 ohms. If not, replace the sending unit.

    Click image to see an enlarged view

    Fig. Checking the sending unit resistance. The resistance should decrease as the engine temperature increases

  8.  

Specific to:

Mercury Villager 1993-2000

Nissan Quest 1993-2000

  1. With the ignition switch OFF , disconnect the engine wiring harness from the ECT sensor.
  2.  
  3. Connect an ohmmeter between the ECT sensor terminals.
  4.  
  5. With the engine cold and the ignition switch in the OFF position, measure and note the ECT sensor resistance.
  6.  
  7. Connect the engine wiring harness to the sensor.
  8.  
  9. Start the engine and allow the engine to reach normal operating temperature.
  10.  
  11. Once the engine has reached normal operating temperature, turn the engine OFF .
  12.  
  13. Once again, disconnect the engine wiring harness from the ECT sensor.
  14.  
  15. Measure and note the ECT sensor resistance with the engine hot.
  16.  
  17. Compare the cold and hot ECT sensor resistance measurements with those in the chart. If the resistances are not within specifications, replace the sensor.

    Click image to see an enlarged view

    Fig. Disconnect the ECT sensor electrical connector to test the sensor



    Click image to see an enlarged view

    Fig. Another method of testing the ECT sensor is to submerge it in cold or hot water and check resistance



    Click image to see an enlarged view

    Fig. ECT sensor resistance-to-temperature specifications

  18.  

 
label.common.footer.alt.autozoneLogo