Circuit Description

The DTC P0116 Engine Coolant Temperature (ECT) sensor performance diagnostic monitors ECT sensor activity. ECT sensor is a thermistor. A thermistor is a resistor whose value varies with temperature. ECT sensors resistance is high when coolant temperature is cold, and ECT sensors resistance is low when coolant temperature is warm. ECT sensor is wired in series with a fixed resistor in the Powertrain Control Module (PCM). PCM applies 5 volts to ECT sensor. PCM monitors voltage across ECT sensor and converts voltage into a temperature reading. PCM will receive a high voltage input when coolant temperature is cold. PCM will receive a low voltage input when coolant temperature is warm. A DTC P0116 may set if the ECT sensor voltage does not indicate engine coolant temperature has increased sufficiently during engine operation. See TEMPERATURE VS. RESISTANCE  table.