W 3500 L4-5.2L DSL Turbo (2005)
Coolant Temperature Sensor/Switch (For Computer): Description and Operation
Engine Coolant Temperature (ECT) Sensor
The engine coolant temperature (ECT) sensor is installed on the thermostat housing. It is a variable resistor. The ECT sensor has a signal circuit and a
low reference circuit. The ECT sensor measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the ECT
signal circuit and a ground for the ECT low reference circuit. When the ECT sensor is cold, the sensor resistance is high. When the engine coolant
temperature increases, the sensor resistance decreases. With high sensor resistance, the ECM detects a high voltage on the ECT signal circuit. With lower
sensor resistance, the ECM detects a lower voltage on the ECT signal circuit.
