Temperature Sensor Adapter harness for ECUGN/MS3/DIYPNP


Short Guy
Hey all!

Since getting my ECUGN working and posting pretty pictures and videos of it kicking ass, I've gotten a lot of PMs asking a lot of really great questions. The one thing that really seems to be intimidating people on this thing is how to get a two-wire temp sensor connected to the ADC inputs on the ECUGN or any MS3Pro based ECU (MS3 Ultimate, DIYAutotune's PnP, etc). Some of the inputs already have pull-up resistors on the board, but if you want to add more than one sensor past the stock ones, you have to add the pull-up yourself. And even that one extra requires popping the case on the ECUGN and moving a jumper.

So I ordered some parts and put this together:



What is it? It's a standard GM closed element temp sensor with a harness added with the pull-up already integrated. You get three-wires out the back. Black goes to ground, red goes to +5v, yellow goes to an ADC input on your Megasquirt. You will have to extend the three wires yourself to reach whatever location you're putting the sensor in.

The pullup resistor is in the plug, and it's a mil-spec 2.49K metal film resistor that can take the heat in an engine bay.

I have enough parts to make 8 of these. It comes as pictured, with the sensor included. It's the same sensor as the coolant sensor in the intake manifold.

$35 shipped to anywhere in the U.S.A. (If you're outside the U.S., we can deal, it'll just be more to cover the additional shipping)

Now, there's no rocket science behind this harness. The parts add up to almost $16 and I'm including the shipping, so I'm not doing this to get rich. I just thought I could help some people out that aren't quite comfortable figuring out how to add the pull-up. With this harness, your thermister just plugs right into the ECU on the green terminal strip using the ECU's built-in ground and +5v. You don't have to dig through hundreds of pages of forums and MegaManual documentation to make sure you've got the right pullup for the sensor. I already did that for you. No need to try and solder the pullup into the harness in your footwell, either. You can worry about other things.

This harness will also plug right into the open-element air temp sensor used on our cars. Other sensors (like the smaller Saturn water temp sensor) can be adapted by cutting off the sensor plug and splicing onto whatever plug for your sensor. The pullup resistor is the proper one for any sensor that follows the GM impedance curve, which is most of them.

Anyway. If this looks like something that'll help you get up and running faster, PM me and I'll get one heading your way.



William Avila (The Buick Guy)
Just curious as to why you would need this? The Ms3 should read off the factory sensor or at least it has in all the ones I have installed. It looks pretty neat but I guess I am confused


Short Guy
Just curious as to why you would need this? The Ms3 should read off the factory sensor or at least it has in all the ones I have installed. It looks pretty neat but I guess I am confused

Excellent question!

The stock ECUGN and the DIYPnP have pull-ups for the factory coolant and intake air sensors built in, yes. You don't need this if you're only going to use those sensors.

But if you want to add more, like a second IAT ahead of the intercooler, or transmission fluid or engine oil temp, you need something like this to convert the 2-wire's impedance based signal to 0-5v signal the ADCs can read directly.

For example, I've got the factory water and intake air temp, but I also added transmission and oil temp, and I'm going to add an addititional intake temp ahead of the intercooler so I can log my intercooler's efficiency. All of those extra temp sensors require a pull-up to work with the inputs.