Coolant Temperature Sensor/Switch (For Computer): Description and Operation

DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor (a resistor which changes value based on temperature) mounted in the engine coolant stream. Low coolant temperature produces a high resistance (100,000 ohms at -40°C/-40°F), while high temperature causes low resistance (70 ohms at 130°C/266°F).

OPERATION
The PCM supplies a 5 volt signal to the ECT sensor through a resistor in the PCM and monitors the terminal voltage. Since this forms a series circuit to ground through the ECT sensor, high sensor resistance (low temperature) will result in high PCM terminal voltage. When the ECT sensors resistance is low (high temperature), the terminal voltage will be drawn lower. This terminal voltage indicates engine coolant temperature to the PCM.

CIRCUIT FAULTS
A hard fault in the ECT sensor circuit should set either a DTC P0117 or P0118. An intermittent failure in the ECT sensor circuit should set either a P1114 or P1115. Remember, these DTCs indicate a fault in the engine coolant temperature circuit, so proper use of the DTC table will lead to either repairing a wiring problem or replacing the sensor, to properly repair a problem.