Circuit Description

WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

The engine coolant temperature (ECT) sensor is a thermistor. A thermistor is a resistor whose value varies with temperature. The ECT sensors resistance is high when the coolant temperature is cold, and the ECT sensors resistance is low when the coolant temperature is warm. The ECT sensor is wired in series with a fixed resistor in the powertrain control module (PCM). The PCM applies 5 volts to the ECT sensor. The PCM monitors the voltage across the ECT sensor and converts the voltage into a temperature reading. The PCM will receive a high voltage signal when the coolant temperature is cold. The PCM will receive a low voltage signal when the coolant temperature is warm. If the ECT sensor voltage does not indicate that the engine coolant temperature has increased sufficiently during engine operation, this DTC sets.

The following table illustrates the difference between temperature, resistance, and voltage:

DTC P1126

Temperature	ECT Resistance	ECT Signal Voltage
Cold	High	High
Warm	Low	Low