coolant temp sensor, theory of operation

[geostar]

I am looking at my new, green, coolant temperature sensor and I would like to know if anyone has a pinout diagram. I suspect that two of the 4 pins are for an RTD and the other 2 are for a contact closure thermostat. I would like to be able to bench test the sensor with a multimeter.

How is this sensor used? My Vag Com has a 01039 Coolant Sensor G2 error, although the dashboard temp gauge is normal, and I do not have any red coolant light illuminated.

 

[PB_NB]

It is my understanding that the CTS is used to send signals to the ECU. It tells the ECU what the engine coolant temperture so the ECU can adjust its fuel mapping and quantity and Injection Pump timing.

It works on a simple variable resistor that lessens as the temp reaches normal operating temperature.

The CTS doesn't control the Temperature guage or the Low Coolant warning light.

Earlier CTS units have only 2 leads coming off. I am not too sure why the newer ones have 4 leads but I can speculate the newer ECU's have a more soffisicated use of the resistance taken from the CTS.

You should be able to test the unit by referring to the Temp to Ohms chart in your Bentley manual.

 

[pruzink]

There are 2 separate temp sensors, one feeds the temp gauge, the other the computer.