Coolant Temperature Sensor (CTS)

The CTS is a thermistor-type sensor located in engine coolant stream. A low coolant temperature will produce a high resistance of approximately 100k ohms at -40°F (-40°C), as temperature rises, resistance will drop to approximately 70 ohms at 266°F (130°C).

ECM supplies and monitors a 5-volt reference signal to the sensor. When temperature is low and resistance is high, the signal voltage remains high. As coolant temperature increases, resistance drops and allows the 5-volt signal to flow through the resistor which lowers signal voltage. Engine coolant temperature affects most systems that are ECM controlled.