Note. For circuit reference, see WIRING DIAGRAMS article.
Circuit Description
Engine Coolant Temperature (ECT) sensor is a thermistor in series with a fixed resistor in PCM. PCM applies 5 volts to ECT sensor. PCM monitors voltage across ECT sensor and converts it into a temperature reading. When coolant temperature is cold, ECT sensor resistance is high (PCM monitors high voltage input). When coolant temperature is warm, ECT sensor resistance is low (PCM monitors low voltage input).