At key-on, the Powertrain Control Module (PCM) sends out a regulated 5 volt signal to the ECT sensor. The PCM then monitors the signal as it passes through the ECT sensor to the sensor ground (sensor return).When the engine is cold, the PCM will operate in Open Loop cycle. It will demand slightly richer air-fuel mixtures and higher idle speeds. This is done until normal operating temperatures are reached.The PCM uses inputs from the ECT sensor for the following calculations: For engine coolant temperature gauge operation through CCD or PCI (J1850) communicationsInjector pulse-widthSpark-advance curvesASD relay shut-down timesIdle Air Control (IAC) motor key-on stepsPulse-width prime-shot during crankingO2 sensor closed loop timesPurge solenoid on/off timesEGR solenoid on/off times (if equipped)Leak Detection Pump operation (if equipped)Radiator fan relay on/off times (if equipped)Target idle speed