An ECT sensor is checked for proper operation. While the voltage is being monitored on the scan tool after a cold start, what should the voltage do as the sensor heats up?

The correct answer indicates that the voltage from the Engine Coolant Temperature (ECT) sensor should steadily decrease as the engine warms up after a cold start. The ECT sensor is a type of thermistor, which means its resistance changes with temperature. When the engine is cold, the coolant is also cold, leading to a higher resistance in the sensor circuit, which translates to a higher voltage reading in the system. As the engine and coolant heat up, the resistance of the ECT sensor decreases, resulting in a lower voltage reading that is sent to the engine control module (ECM).

This relationship between temperature and voltage is critical for engine management systems, as it helps the ECM make appropriate adjustments to fuel delivery and ignition timing to optimize performance and emissions. Monitoring this change during a cold start is essential for diagnosing potential issues with the sensor or the cooling system itself. Understanding this concept is vital for anyone working in advanced engine performance and diagnostics.