Engine Coolant Temperature Sensor

1. Powertrain Control Module (PCM)
2. Throttle Position (TP) sensor
3. Mass Air Flow (MAF) sensor
4. Intake Air Temperature (IAT) sensor
5. Idle Air Control (IAC) valve
6. Engine Coolant Temperature (ECT) sensor
7. Heated Oxygen Sensor (HO2S)
8. Camshaft Position (CMP) sensor
9. Knock Sensor (KS)
10. Vehicle Speed Sensor (VSS)
11. Crankshaft Position (CKP) sensor
12. Fuel Injector
13. Coolant Temperature Sensor (CTS)
14. Exhaust Gas Recirculation (EGR)
15. Manifold Absolute Pressure (MAP)

Source: FreeAutoMechanic.com/car-engine-sensors.html

Engine Coolant Temperature (ECT)

The engine coolant temperature sensor resistance changes in response to engine coolant temperature. The sensor resistance decreases as the surrounding temperature increases. This provides a reference signal to the PCM, which indicates engine coolant temperature.

The following symptoms can be caused by a faulty Engine Coolant Temperature Sensor or circuit loose connections.