Mitsubishi Pick-ups and Montero 1983-1995 Repair Guide

Engine Coolant Temperature Sensor

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OPERATION



See Figures 1 and 2

The Engine Coolant Temperature sensor (ECT), located on the intake manifold of the engine, converts the temperature of the coolant in the engine to voltage, and inputs this voltage to the ECM. The ECM uses these signals to help it decide how to regulate the MFI system components.



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Fig. Fig. 1: The location of the Engine Coolant Temperature (ECT) sensor-3.0L and 3.5L engines



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Fig. Fig. 2: The location of the Engine Coolant Temperature (ECT) sensor-2.4L engines

Since the ECT is a type of resistor, the electrical current flowing through the sensor from and to the ECM is changed by the temperature of the coolant. The hotter the coolant becomes, the lower the resistance created by the ECT sensor.

If, during engine warm up, the fast idling speed is not correct, or black smoke is emitted, the problem is usually a malfunction of the ECT sensor.

HARNESS TESTING



See Figures 3, 4 and 5

The 1993-95, rear-wheel drive 2.4L (California) Pick-ups have the same engine controls as the 3.0L engines. All other 2.4L engines are listed as 2.4L engines.



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Fig. Fig. 3: The ECT harness testing procedure-2.4L engines



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Fig. Fig. 4: The ECT harness testing procedure-3.0L (12 valve) engines

  1. Unplug the ECT sensor wire connector form the ECT sensor. Check terminal 1, for 2.4L engines, or terminal 2, for all 3.0L and 3.5L engines, of the connector for continuity to ground. If there is no continuity the problem lies in the wire harness, repair or replace the harness between the following terminals:
    1. 2.4L engines: ECT terminal 1 and ECM terminal 14.
    2.  
    3. 3.0L (12 valve) engines: ECT terminal 2 and ECM terminals 17 and 24.
    4.  
    5. 3.0L (24 valve) and 3.5L engines: ECT terminal 2 and ECM terminal 72.
    6.  

  2.  
  3. This step is for all engines except for the 2.4L. Unplug the ECM harness connector. Check for an open or short circuit between the following ECT sensor and ECM terminals:
    1. 3.0L (12 valve) engines: ECT terminal 1 and ECM terminal 20.
    2.  
    3. 3.0L (24 valve) and 3.5L engines: ECT terminal 1 and ECM terminal 63.
    4.  

  4.  



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Fig. Fig. 5: The ECT harness testing procedure-3.0L (24 valve) and 3.5L engines

  1. Make sure the ECM harness connector is plugged in. Turn the ignition switch to ON and measure the power supply from terminal 2 (2.4L) or terminal 1 (3.0L and 3.5L) of the ECT harness connector. If the voltage is not 4.5-4.9 volts, replace the ECM itself, otherwise the harness and ECM are good.
  2.  

Before replacing the ECM or other computer module, either check or have the component in question checked.

COMPONENT TESTING



See Figure 6

This procedure is the same for all engine models.

  1. Remove the ECT sensor from the intake manifold. Be careful not to damage the plastic portion or the electrodes of the ECT sensor when unscrewing the sensor from the manifold.
  2.  



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Fig. Fig. 6: Place the ECT sensor into a pot of water and measure the resistance of its two terminals while heating the water

  1. With the temperature sensing portion of the ECT sensor immersed in water, check the resistance between the two terminals. Slowly heat the water up and watch to see the change in resistance. With the water at 32°F (0°C) the resistance should be 5.9 kilohms, at 68°F (20°C) the resistance should be 2.5 kilohms, at 104°F (40°C) the resistance should be 1.1 kilohms, and at 176°F (80°C) the resistance should be 0.3 kilohms. If the resistance deviates from the standard value greatly, replace the sensor with a new one.
  2.  

REMOVAL & INSTALLATION



  1. To remove the ECT sensor, unplug the harness connector from the top of the sensor.
  2.  
  3. Use a socket or wrench to remove the sensor from the intake manifold. Make sure not to damage the plastic portion or the electrodes on the sensor.
  4.  

To Install:
  1. Clean the threads of the ECT sensor. Apply 3M®Nut Locking Part No. 4171 sealant or the equivalent to the threaded portion of the sensor.
  2.  
  3. Screw the sensor into the intake manifold, making certain not to crossthread the sensor. Tighten the ECT sensor to 15-29 ft. lbs. (20-40 Nm).
  4.  
  5. Fasten the harness connector back onto the top of the ECT sensor.
  6.  

 
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