Engine Coolant Temperature (ECT) Sensor

ECT Circuit (Typical):

Engine Coolant Temperature Sensor:

PURPOSE
The PCM uses the engine coolant temperature sensor to delay Torque Converter Clutch (TCC) operation and adjust line pressure until the engine has warmed up.

OPERATION
The Engine Coolant Temperature (ECT) sensor is a thermistor (a resistor that changes value based on temperature) mounted in the engine coolant stream. Low engine coolant temperature produces a high resistance and high engine temperature causes a low resistance.

The PCM supplies a 5 volt signal to the ECT sensor through an internal resistor then measures the voltage drop in the circuit. Voltage will be high when the engine is cold and low when the engine is hot.

DTC 14 or DTC 15 indicates a failure in the engine coolant temperature circuit. Most scan tools display engine coolant temperature in degrees Centigrade. After the engine has started, the temperature should rise steadily to about 90°C then stabilize when the thermostat opens. If a fault occurs, the PCM will substitute a value and the scan tool will display at the high end of the range. When the circuit resumes normal operation, the PCM will again recognize ECT readings.