Free ASE Certification from my Smog License Repair Course: Engine-Coolant-Temperature-Sensor
BAR Specific Diagnostic Class
An Engine-Coolant-Temperature-Sensor changes resistance with temperature, this is a key element for the on board computer circuit for close loop operation.
As the temperature rises the resistance drops, or as the temperature drops the resistance rises.
This is a two wire sensor that has it’s own 5 volt supply from the PCM
The PCM will watch a voltage drop across the second resistor “ECT” and that number will determine if the vehicle is hot or cold.
ASE L1 Related Information Below
This portion of this page is additional information along with the top portion for the L1 portion of the test.
As stated above the coolant sesnor is temperature driven. As the temperature changes, the temperature changes the resistance of the sensor also changes and so does the voltage drop that is register at the ECM/PCM.
Remember the resistance and the voltage drop affects the ECM/PCM command back to the injectors.
Here is an example if the resistance increases in an NTC circuit, the ECM/PCM will interpret this as a cold engine and increase the pulse width.
The additional resistance can be corrosion on a connector, loose or frayed wires or the coolant sensor itself.