How to read the voltage comming out the ECT (Engine Coolant Temperature)?

[Markino]

Hi guys,
I've read that the ECT sensor has a wire where we can read the coolant temperature: the ECT is a variable resistor and in the P/W wire there is a variable voltage from 0 to ~5V that can be converted to temperature.
Do you know how the ECT works and how to calculate the temperature from the voltage? Is there a voltage divider or stuff like that?

 

[OneGun]

If it is a 2-wire sensor, it is likely what is known as a "thermistor". Most are what is called NTC (Negative Temperature Coefficient). That means as temperature increases, resistance decreases.

In any case, most thermistors are calibrated to have a voltage range that equates to different temperature readings... so they're not all the same. A reading of 0 volts on this sensor may equate to 0°C where as a full 5 volts (or close to it) might be somewhere around 110°C. That seems like a normal range.

If you are interested in seeing how the voltage changes, you can backprobe the connector while it's still plugged in and check it with a volt meter. Put the ground lead of your meter on any ground, then probe whatever you used to backprobe with the read lead. Of course, you'll need to figure out which wire is the signal and which is the ground (return).

But like I said, unless you can find any info on that specific sensor's range and it's voltage-to-temp correlation, those voltage readings won't mean much to you.

 

[Brillot2000]

I am sure that only the engineer that developed that system would know for sure, however Honda is not sharing that information with the public. There might be some mentions in the Honda Shop Manual for Troubleshooting the sensor. As for a formula to convert V to T°, I am sure that information cannot be found anywhere.

 

[showkey]

The standard for Honda is usually 2.8 to 3.0 volts equals 70*F. Near "5" volts is colder and near "0" volts is hotter and voltage is pretty much linear over the entire range. About .6-.7 volts is about normal operating temperture is most vehicles.

Common values used by Honda

 

[lootzyan]

ECT sensor resistance for NC700, CTX700 (by Service Manual)

40°C (104°F) - 1.0 – 1.3 kΩ
100°C (212°F) - 0.1 – 0.2 kΩ