Alero L4-144 2.4L DOHC VIN T SFI (2000)
Coolant Temperature Sensor/Switch (For Computer): Description and Operation
The Engine Coolant Temperature (ECT) sensor (3) is a thermistor, a resistor which changes value based on temperature, mounted in the engine coolant
stream. A low coolant temperature produces a high resistance of 100,000 ohms at -40°C (-40°F), while a high temperature causes a low resistance of 70
ohms at 130°C (266°F).
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 will result in high PCM terminal voltage. When the resistance of the ECT sensor is low, the
terminal voltage will be drawn lower. This terminal voltage indicates engine coolant temperature to the PCM.
A hard fault in the ECT sensor circuit should set either a DTC P0117 or P0118. Remember, these DTCs indicate a malfunction in the engine coolant
temperature circuit, so proper use of the DTC table may lead to either repairing a wiring problem or replacing the sensor, to properly repair a problem.
