Coolant Temperature Sensor (CTS)

CTS 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).

ECM supplies a 5-volt reference signal through an internal resistor to CTS and measures return voltage. Voltage is high when coolant temperature is low, and low when coolant temperature is hot. By measuring voltage, ECM knows engine coolant temperature. Engine coolant temperature affects cold advance and glow plug systems.