The engine coolant temperature (ECT) sensor is a thermistor that varies resistance according to changes in engine coolant temperature. The ECM supplies a 5 volt reference through a pull-up resistor(s) to the sensor, which is connected to ground. When the sensor is cold it has a high resistance (high signal voltage at ECM). As the sensor temperature increases, its resistance decreases (low signal voltage at ECM). The ECM uses the signal voltage to determine engine coolant temperature. DTC P0115 sets when the calculated accumulated airflow exceeds the predicted accumulated airflow when the engine coolant temperature has reached a calibrated temperature (more air will flow through a cold engine then when the engine is warm).

DTC P0115 indicates lower than normal engine coolant temperature, which most likely was NOT caused by a short/open or intermittent short/open in the ECT wiring.

Possible causes of low engine coolant temperature:

ECT sensor reading may be compared to IAT sensor reading on Scan tool after the vehicle has been sitting longer than 6 hours with the ignition Off. Both readings should be within 6°C or 10°F of each other.

Refer to ECT General Description for a Temperature vs. Resistance chart.