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    Suzuki Samurai/Sidekick/Tracker 1986-1998 Repair Guide

    Engine Coolant Temperature (ECT) Sensor/Switch

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    OPERATION



    Carbureted Engine

    The Engine Coolant Thermal (ECT) switch, often referred to as simply the thermal switch, provides temperature information to the ECM for driveability. The ECT switch opens and closes depending on the engine coolant temperature. The switch is closed when the engine is cold, and opens when the engine warms to above 116°F (46.5°C). The ECM monitors the ECT switch circuit, and knows the engine is warmed up when the circuit registers infinite resistance (the switch is open).

    Fuel Injected Engines

    The Engine Coolant Temperature (ECT) sensor is a thermistor (a resistor which changes its value based on the temperature it encounters) mounted in a coolant passage. Low coolant temperature produces a high resistance, while high temperature causes a low resistance.

    The ECM supplies a 5 volt reference signal to the ECT through a resistor in the ECM, and measures the voltage. By measuring the voltage the ECM calculates the engine coolant temperature. Engine coolant temperature affects most systems that are controlled by the ECM.

    A failure in the ECT sensor should set a Diagnostic Trouble Code (DTC). Remember that these DTC's indicate a failure somewhere in the ECT circuit, so proper use of the component testing will either lead to repairing a wiring problem, replacing the sensor and/or replacing the ECM to properly repair the fault.

    The ECT used on the 1.6L TFI engine is located on the right-hand side of the engine, mounted in the intake manifold.

    The ECT sensor used on 1.6L MFI engines is mounted in the intake manifold, next to the thermostat housing.

    TESTING



    Carbureted Engine

    See Figures 1 and 2

    1. Drain the engine coolant into a large catch pan.
    2.  
    3. Remove the ECT switch from the intake manifold.
    4.  
    5. Position the switch and a thermometer in a container of cold water (86°F/30°C or below) on a stove.
    6.  
    7. Using an ohmmeter, measure the resistance between the two switch terminals. There should be continuity, because the switch should be closed.
    8.  



    Click image to see an enlarged view

    Fig. Fig. 1: To test the ECT sensor/switch, position the sensor/switch in a container of cold water and note the resistance (for sensors) or continuity (for switches)



    Click image to see an enlarged view

    Fig. Fig. 2: Heat the container of water and once again note the resistance (sensor) or continuity (switch)-replace the sensor/switch if it does not perform as specified

    1. Slowly heat the water in the container to above 116°F (46.5°C) and check the resistance once again. There should now be no continuity (infinite resistance).
    2.  
    3. If the switch functioned as described, it is good. Otherwise, replace it with a new one.
    4.  
    5. Install the switch and fill the engine cooling system.
    6.  

    Fuel Injected Engines

    See Figures 1, 2 and 3

    The ECT sensor may be tested by measuring the temperature-to-resistance values with an ohmmeter. A cold ECT sensor should have a high resistance value, whereas a warm sensor should exhibit a low resistance value.

    Some models may be equipped with ECT sensors with three wire terminals. On these vehicles, terminals A and B are the signal terminals, and terminal C supplies voltage to the coolant temperature gauge in the instrument cluster.

    1. Drain the engine coolant into a large catch pan.
    2.  
    3. Perform a visual inspection of the ECT sensor connector to ensure that it is properly engaged, and that there are no bent, corroded, loose or damaged terminals.
    4.  



    Click image to see an enlarged view

    Fig. Fig. 3: The resistance of the sensor should change inversely from the temperature of the water-if the resistance of the ECT sensor does not approximately match the values shown in the chart, replace the sensor

    1. Remove the ECT sensor from the intake manifold.
    2.  
    3. Position the sensor and a thermometer in a container of cold water (86°F/30°C or below) on a stove.
    4.  
    5. Using an ohmmeter, measure and note the resistance between the two ECT sensor terminals (A and B on three-terminal sensors). Also note the temperature of the water.
    6.  
    7. While observing the ohmmeter and thermometer, slowly heat the water in the container. The resistance of the sensor should smoothly decrease as the water temperature increases, and should match the accompanying chart.
    8.  
    9. If the sensor resistance values match those in the accompanying resistance table, and if the resistance changed smoothly while warming the water, the sensor is good. Otherwise, replace the ECT sensor with a new one.
    10.  
    11. Install the switch and fill the engine cooling system.
    12.  

    REMOVAL & INSTALLATION



    1. Disconnect the negative battery cable.
    2.  
    3. Drain the engine coolant into a large catch pan until it is below the level of the sensor/switch.
    4.  
    5. Detach the wiring harness connector from the sensor/switch.
    6.  
    7. Using a deep socket or crowfoot and ratchet, remove the ECT sensor/switch from the intake manifold.
    8.  

    To install:
    1. If the old ECT sensor/switch is going to be reinstalled, clean the threads thoroughly.
    2.  
    3. Apply silicone sealant on, or wrap Teflon® sealing tape around, the sensor/switch threads.
    4.  
    5. Thread the sensor/switch into the intake manifold by hand until finger-tight, then tighten it to 9-12 ft. lbs. (12-17 Nm).
    6.  
    7. Reattach the wiring harness connector to the sensor/switch. Push the connector onto the terminal until an audible click is heard, then pull back gently to ensure that it is fully engaged.
    8.  
    9. Fill the engine cooling system.
    10.  
    11. Connect the negative battery cable.
    12.  
    13. Start the engine and inspect for coolant leaks. Ensure proper ECT sensor/switch operation.
    14.  

     
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