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

Engine Coolant Temperature (ECT) Sensor:

PURPOSE
The Engine Coolant Temperature (ECT) sensor provides an input to the Powertrain Control Module (PCM). The PCM uses engine coolant temperature data to adjust the fuel injection base pulse width, EGR flow, and ignition timing.

CONSTRUCTION
The ECT is a two lead thermistor type sensor with a negative temperature coefficient.

Descriptive Schematic:

OPERATION
The PCM applies a 5.0 volt reference voltage to the ECT signal lead while the signal return lead is connected to a common sensor ground.

As the temperature of the engine coolant increases the resistance of the ECT sensor decreases and correspondingly the voltage drop across the ECT sensor is reduced.

A decrease in engine coolant temperature will increase the resistance of the ECT and raise the voltage drop across the sensor.

The normal operating range of the ECT is 3.50 volts (50°F) to 0.35 volts (230°F).

Due to its negative temperature coefficient, poor electrical connections or minor increases in resistance across the ECT circuit harness and ground connections can result in temperature values that are lower than actual.

RELATED DIAGNOSTIC TROUBLE CODES

DTC 116 - The ECT sensor output is out of self-test range, 0.3-3.7 volts.

DTC 117 - The ECT sensor output is less than the self-test minimum, 0.2 volts.

DTC 118 - The ECT sensor output is greater than the self-test maximum, 4.6 volts.