Toyota Pick-ups/Land Cruiser/4Runner 1989-1996

Engine Coolant Temperature (ECT) Sensor

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OPERATION



The ECT is a thermistor (a resistor which changes value based on temperature) mounted in the engine coolant stream. As the temperature of the engine coolant changes, the resistance of the coolant sensor changes. Low coolant temperature produces a high resistance: 100,000 ohms at -40°F (-40°C). High temperature causes low resistance: 70 ohms at 284°F (140°C).

The ECM supplies a 5 volt signal to the coolant sensor and measures the voltage that returns. By measuring the voltage change, the ECM determines the engine coolant temperature. The voltage will be high when the engine is cold and low when the engine is hot. This information is used to control fuel management, IAC, spark timing, EGR, canister purge and other engine operating conditions.

TESTING



See Figures 1 and 2

  1. Remove the ECT sensor from the engine.
  2.  
  3. Fill a clean container with water and measure its temperature.
  4.  
  5. Place the sensor tip into the water. Measure the resistance of the ECT sensor with an ohmmeter. Compare the resistance with the temperature as per the graph.
  6.  



Click image to see an enlarged view

Fig. Fig. 1: Submerge the end of the temperature sensor in cold or hot water and check resistance



Click image to see an enlarged view

Fig. Fig. 2: Temperature sensor resistance graph

  1. If it is not within specifications, replace the sensor.
  2.  
  3. Install the ECT sensor.
  4.  

REMOVAL & INSTALLATION



Excluding 5VZ-FE Engine
  1. Drain the engine cooling system.
  2.  
  3. Disconnect the engine wire protector from the brackets if used.
  4.  
  5. Detach the ECT sensor wiring.
  6.  
  7. Using a deep socket, remove the ECT sensor and gasket.
  8.  

To install:
  1. Using a new gasket and deep socket, install the ECT sensor. Tighten to 14 ft. lbs. (20 Nm).
  2.  
  3. Connect the ECT wiring to the sensor.
  4.  
  5. Install the engine wire protector to the brackets if used.
  6.  
  7. Fill the cooling system, start the engine, top off the system.
  8.  

5VZ-FE Engine

  1. Drain the engine cooling system.
  2.  
  3. Disconnect the upper radiator hose from the water outlet.
  4.  
  5. Disconnect the power steering air hose from the clamp.
  6.  
  7. Disconnect the three cord clamps of the spark plug wires from the belt cover.
  8.  
  9. Remove the mounting bolts for the timing belt cover and gasket.
  10.  
  11. Disconnect the camshaft position sensor harness.
  12.  
  13. Remove the fuel pipe.
  14.  
  15. Disconnect the ECT sensor harness.
  16.  
  17. Using a 19mm deep socket, remove the sensor and gasket.
  18.  

To install:
  1. Using a new gasket and deep socket, install the ECT sensor. Tighten to 14 ft. lbs. (20 Nm).
  2.  
  3. Connect the ECT wiring to the sensor.
  4.  
  5. Reinstall the fuel pipe with four new gaskets, tighten to 25 ft. lbs. (34 Nm).
  6.  
  7. Attach the timing belt cover, tighten to 80 inch lbs. (9 Nm).
  8.  
  9. Reconnect the upper radiator hose to the water outlet.
  10.  
  11. Fill the cooling system, start the engine, top off. Check for leaks.
  12.  

 
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