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2.49K pull up vs. 100k pull up?

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posted this in EFI wiring.. but no love.. so posting here..

Long story short... working on pinning my AEM infinity 6. Pin C1-39 is AIT sensor 5V A/D 2.49K pull up Analog input.

Bad news:

I broke the pin retainer lever in the connector. and leaves it loose in the connector. This concerns me about intermittent connection issues.

Good news:

There are spare Analog inputs on other pins of the ECU. For this question I will pick Pin C1-75 which is 5V A/D 100K pull up Analog input.


Will moving the AIT sensor in from an Analog 2.49K pull up 5V A/D on Pin C-39 to Analog C1-75 5V A/D 100K pull up work. I understand I will need to configure the AIT to point at the new pin in Infinity tuner. How will going from a 2.49K pull up to a 100K pull up effect that signal to the ECU. or will it matter at all?

Thank you in advanced for your input


Forget about it, 100k is way too much !

Vin = 5V, R1 is your pull up, R2 is your AIT sensor and Vout = Vin x R2/(R1+R2)

Here is what you're going to end up with: (2.49K in black, 100K in blue)

Attached Files

Thank you for the reply!

Next question.. What use are the 100k pull up inputs for 0-5v signals then? All of the auxiliary inputs on the infinity are 100k pull up.

For example I was planning on using these aux inputs with dual stand alone O2 sensors (v6) as the infinity has only one O2 controller built in. They are also 0-5v. So I'm in the same spot there? The stand alone Uego has a 0-1v out as well. Would that work better?

Thanks again!


You can just add your own external 2.5k pullup to the analog voltage signal to create the same characteristics as the analog temperature input.

The reason for a 100k pull-up is so that you can detect when nothing is connected to the input, but it's resistance is high enough not to influence the sensors signal. 100k pullups also make it easy to connect a switch directly between in the input and ground.

If your input is a voltage (like a wideband 0-5V analog output) having a 100k pull up doesn't change anything.

Having a pull up simply put the input at 5v if nothing is connected to it.

Thank you all with your patience with lack of knowledge on this, you are all being of a great help.

From David's post I think I understand. I will just repeat what I'm hearing to be sure...

I will take the 0-5V signal wire from the Uego controller, connect a 2.49K resistor prior to the ecu pin, then connect from the resistor to the ECU pin that already has an internal 100K pull up.

Again thank you for your patience in helping me through this. It may be very basic to many of you, but it's a first for me.


No. If you connect a 0-5V signal you have nothing to do.

if you connect a temp sensor (like the IAT sensor) you have to add a 2.49k resistor between the 5V output of the ECU (used for things like the TPS) and the signal input.

Also, if you want accurate measurement, you will have to re-calibrate the IAT (except if you can find a 2553 Ohms resistor)

Ok I guess where I was getting confused was.. I though the output from the AIT was 0-5 volts... unlike the uego controller that is a true 0-5V.

Your AIT sensor is just a resistor that varies with temperature. To get a variable voltage from this you need to provide the pull-up resistor to the voltage reference (5V). The drawing provided by Ludo describes this clearly, and shows you the math.

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