Engine Coolant Temperature or ECT sensor

ECT sensor is a very important for engine cold start and an open loop running of the engine. Its a negative temperature coefficient, which means the colder the sensor the more resistance it produce, the hotter the temperature the less resistance. This sensor determine injectors cold start duty cycle.Here is a graph showing different resistance reading at different temperatures. This sensor decrease resistance value with hotter temperature. So if we use 5 volts power supply to the sensor and connect it to ECU it can see different voltage input signal with different temperatures and tell ECU when ever engine hot, cold or warm.

Intake Air Temperature sensor works the same way so ECT and IAT can be checked same way.