Engine Coolant Temperature Sensor

WARNING: This page is about a different car, the 2003 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.

The Engine Coolant Temperature (ECT) sensor is a thermistor (temperature sensitive resistor) located near engine coolant outlet on engine block. The ECM supplies and monitors a 5-volt signal to ECT sensor. This monitored 5-volt signal is then modified by resistance of the ECT sensor. When coolant temperatures are low, ECT sensor resistance is high and the ECM sees a high monitored voltage signal. When coolant temperatures are high, ECT sensor resistance is low and the ECM sees a low monitored voltage.

Coolant temperature input is used in the control of fuel delivery, ignition timing, idle speed and emission control devices. An ECT sensor which is out of calibration will not set a DTC, but can cause fuel delivery and driveability problems. An ECT sensor circuit problem should set a related DTC. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 3.2L CTS article.