The Engine Coolant Temperature (ECT) sensor is used to sense engine coolant temperature. The sensor protrudes into an engine water jacket.
The ECT sensor is a two-wire Negative Thermal Coefficient (NTC) sensor. Meaning, as engine coolant temperature increases, resistance (voltage) in the sensor decreases. As temperature decreases, resistance (voltage) in the sensor increases.
The PCM uses inputs from the ECT sensor for the following calculations:
For engine coolant temperature gauge operation through CAN Bus communications
ASD relay shut-down times
Idle Air Control (IAC) motor key-on steps
Pulse-width prime-shot during cranking
O2 sensor closed loop times
Purge solenoid on/off times
Cooling fan control
Temperature gauge operation
A/C cutoff at high coolant temperatures
EGR solenoid on/off times (if equipped)
Leak Detection Pump operation (if equipped)
Radiator fan relay on/off times (if equipped)
Target idle speed