Engine Coolant Temperature (ECT) Sensor

ECT sensor is a thermistor (temperature sensitive resistor). A coolant temperature of -40°F (-40°C) produces a high resistance (100,000 ohms), while a 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 knows engine coolant temperature. Engine coolant temperature affects injector timing, cold advance, EGR, glow plug system, transmission shifts and TCC.