Engine Coolant Temperature Sensor

The Engine Coolant Temperature (ECT) sensor is a thermistor (temperature sensitive resistor). An engine coolant temperature of -40°F (-40°C) produces a high resistance (100 k/ohms), while an engine coolant temperature of 266°F (130°C) produces a low resistance (70 ohms).

PCM supplies a 5-volt reference signal through an internal resistor to ECT sensor and measures return voltage. Voltage is high when coolant temperature is low, and low when coolant temperature is hot. By measuring voltage, PCM can determine engine coolant temperature. Engine coolant temperature affects injector timing and glow plug system.