Coolant Temperature Sensor
An electronic sensor that measures the temperature of the engine coolant, helping the engine computer regulate fuel delivery, ignition timing, and cooling fans.
The engine coolant temperature (ECT) sensor is a thermistor located near the thermostat housing or cylinder head. As the engine coolant temperature changes, the sensor's electrical resistance changes, sending a corresponding voltage signal to the engine control module (ECM).
The ECM uses this signal to adjust the fuel-air mixture (richer when cold, leaner when warm), manage ignition timing, control variable valve timing, and trigger the electric radiator cooling fans. It also drives the temperature gauge on the dashboard.
A failed ECT sensor can cause the engine computer to assume the engine is always cold or always hot, leading to poor fuel economy, engine overheating, rough idling, black exhaust smoke, or cooling fans running constantly. Replacing a failed sensor is critical for smooth engine management.