Negative Temperature Coefficient Sensors
An (ECT) Engine Coolant Temperature sensor is a thermistor; a material that changes electrical resistance along with changes in temperature. It’s actually an NTC or negative temperature coefficient sensor. When the engine is first started the coolant is cold. The temperature sensor adds high resistance to the circuit creating a greater difference in voltage between the 5 volt reference circuit and the ground circuit. This difference between the two is measured by the PCM and actuator outputs are made according to this sensor’s input.
As the engine reaches operating temperature the resistance of the sensor is less and the difference between the two circuits grows closer. The PCM recognizes this input and activates components like the engine’s cooling fans to maintain proper operating temperature. The PCM uses different strategies programmed into its lookup tables for hot and cold operating conditions. This signal will affect EGR flow, enrich fuel mixtures, and delay torque converter or A/C compressor engagement. Excessive resistance in the connector or anywhere in this circuit will alter the signal to the PCM, increasing injector pulse width and advancing the engine’s ignition timing.