DTC P0125: ECT Excessive Time To Enter Closed Loop: Description
WARNING: This page is about a different car, the 2002 Saturn LW200, 2002 Saturn L200, and 2002 Saturn L100. However, it is still accessible from the selected car via links, so may be relevant.
Engine Coolant Temperature (ECT) sensor is a thermistor (resistance changes as engine coolant temperature changes) in series with a fixed resistor within PCM. PCM supplies a 5-volt reference voltage to ECT sensor. As temperature changes, ECT sensor resistance changes, which changes voltage.
As engine coolant temperature decreases, ECT sensor resistance increases. As engine coolant temperature increases, ECT sensor resistance decreases. PCM monitors voltage input from ECT sensor and converts it into a temperature value. DTC will set when calculated accumulated airflow exceeds predicted accumulated airflow when engine temperature has reached a calibrated temperature. More air will flow through a cold engine than when engine is warm.