The Engine Coolant Temperature (ECT) sensor is mounted in the intake manifold and sends engine temperature information to the ECM. The ECM supplies 5 volts to the coolant temperature sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the ECM monitors a high signal voltage which it interprets as a cold engine. As the sensor warms (internal resistance low), the ECM monitors a low signal voltage which it interprets as warm engine.
See Figures 1 and 2
- Remove the ECT sensor from the vehicle.
- Immerse the tip of the sensor in container of water.
- Connect a digital ohmmeter to the two terminals of the sensor.
- Using a calibrated thermometer, compare the resistance of the sensor to the temperature of the water. Refer to the engine coolant sensor temperature vs. resistance illustration.
- Repeat the test at two other temperature points, heating or cooling the water as necessary.
- If the sensor does not meet specification, it must be replaced.
REMOVAL & INSTALLATION
See Figure 3
- Disconnect the negative battery cable.
- Drain the cooling system below the level of the sensor and disengage the sensor electrical connection.
- Remove the coolant sensor.
- Install the sensor and engage the electrical connector.
- Refill the cooling system and connect the negative battery cable.