Circuit Description

The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage to the Engine Control Module (ECM). The ECM supplies a voltage on the signal circuit to the sensor. The output varies as the ECT increases. At normal engine operating temperature, the voltage will be between 1.5 and 4 volts at the ECT signal terminal.

When the vehicle is first started, the ECM monitors the ECT and determines if it reaches a specified temperature level within a predetermined time. The time is based on Intake Air Temperature (IAT) and the startup ECT.