DTC P0115: ECT Sensor Circuit: Description

The DTC P0115 Engine Coolant Temperature (ECT) Sensor Circuit diagnostic detects an out of range sensor signal. The ECT sensor is a thermistor. A thermistor is a resistor whose value varies with the temperature. The electrical resistance of the ECT sensor is high when the coolant temperature is cold, and the 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). PCM applies 5 volts to the ECT sensor. PCM monitors the voltage across the ECT sensor and converts the voltage into a temperature reading. The voltage measured by the PCM will be high when the coolant temperature is cold, and low when the coolant temperature is warm.