Mazda Trucks 1987-1993 Repair Guide

Engine Coolant Temperature (ECT) Sensor

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OPERATION



The engine coolant temperature sensor resistance changes in response to engine coolant temperature. The sensor resistance decreases as the surrounding temperature increases. This provides a reference signal to the PCM, which indicates engine coolant temperature.

The ECT sensor is mounted on the lower intake manifold near the water outlet/thermostat housing, or on the water outlet/thermostat housing itself.

TESTING



See Figures 1 and 2

  1. Disengage the engine wiring harness connector from the ECT sensor.
  2.  
  3. Connect an ohmmeter between the ECT sensor terminals, and set the ohmmeter scale on 200,000 ohms.
  4.  
  5. With the engine cold and the ignition switch in the OFF position, measure and note the ECT sensor resistance. Attach the engine wiring harness connector to the sensor.
  6.  
  7. Start the engine and allow the engine to warm up to normal operating temperature.
  8.  
  9. Once the engine has reached normal operating temperature, turn the engine OFF
  10.  
  11. Once again, detach the engine wiring harness connector from the ECT sensor.
  12.  
  13. Measure and note the ECT sensor resistance, then compare the cold and hot ECT sensor resistance measurements with the accompanying chart.
  14.  
  15. Replace the ECT sensor if the readings do not approximate those in the chart, otherwise reattach the engine wiring harness connector to the sensor.
  16.  



Click image to see an enlarged view

Fig. Fig. 1: IAT and ECT sensor specifications chart-Navajo models



Click image to see an enlarged view

Fig. Fig. 2: ECT sensor specifications chart-Pick-up and MPV models

REMOVAL & INSTALLATION



See Figure 3

  1. Partially drain the engine cooling system until the coolant level is below the ECT sensor mounting hole.
  2.  
  3. Disconnect the negative battery cable.
  4.  



Click image to see an enlarged view

Fig. Fig. 3: Most ECT sensors (arrow) can be found on the intake manifold, near the water outlet housing

  1. Detach the wiring harness connector from the ECT sensor.
  2.  
  3. Using an open-end wrench, remove the coolant temperature sensor from the intake manifold or thermostat housing.
  4.  

To install:
  1. Thread the sensor into the intake manifold, or thermostat housing, by hand, then tighten it securely.
  2.  
  3. Connect the negative battery cable.
  4.  
  5. Refill the engine cooling system.
  6.  
  7. Start the engine, check for coolant leaks and top off the cooling system.
  8.  

 
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