Engine Coolant Temperature Sensor

The Engine Coolant Temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The Engine Control Module (ECM) supplies 5 volts to the signal circuit, and a ground for the ECT low reference circuit. When the coolant temperatures are low, the resistance is high. When the coolant temperatures are high, the resistance is low. The ECM uses this input for engine controls and enabling criteria for diagnostics. The ECM will record the amount of time the ignition is OFF. At restart, the ECM will compare the temperature difference between the ECT and Intake Air Temperature (IAT). If the temperature difference is not within the calculated amount after the ignition OFF time, DTC P0116 sets. Before failing this test, the ECM will perform a calculation to determine the presence of a block heater.

If the ECM detects an excessively low ECT signal voltage, which is a high temperature indication, DTC P0117 sets. If the ECM detects an excessively high ECT signal voltage, which is a low temperature indication, DTC P0118 sets.