My 2000 2500 is going into 3 cylinder high idle even when its 80ºF out. I do have the high idle switches bit they are set so the truck is getting its true readings. Which sensor is causing this?

IAT sets the mode. ECT cancels the high idle.

Do you know the temperature that it activates each at? I have my code reader on live data and getting IAT temp of 50 when I first started it. And it still is going into three cylinder

3 CYL 15°F IAT

6 CYL 32°F IAT

Remember this is with grid heaters running.

Cancels 170°F ECT

This is all listed in the tsb by Dodge in the article database

Am I right to assume that the IAT temp that shows on the obd2 scanner is the same sensor as the ecm gets it reading from. I ask because if so this is very confusing as the IAT temp was 50 yesterday and the 3 cylinder high idle still was coming on.

1 hour ago, Lund1990 said:

Am I right to assume that the IAT temp that shows on the obd2 scanner is the same sensor as the ecm gets it reading from

I think you are correct. I am basing this on the fact that I am using an IAT fooler (potentiometer) that is adjusted to keep the IAT reading at a constant 143°F. I can tell the ECM responds to the setting because it does not advance the timing aggressively, as it does without the IAT fooler. I don't have the high idle switch on my truck.

Maybe it would be worth completely removing the high idle switch to see if the symptoms change.

• John

13 hours ago, Tractorman said:

I think you are correct. I am basing this on the fact that I am using an IAT fooler (potentiometer) that is adjusted to keep the IAT reading at a constant 143°F. I can tell the ECM responds to the setting because it does not advance the timing aggressively, as it does without the IAT fooler. I don't have the high idle switch on my truck.

Maybe it would be worth completely removing the high idle switch to see if the symptoms change.

• John

I had thought about that, I just figured if I'm able to visually see the values change on the scan tool that the computer must be getting the same values. I'll try unplugging the switches and see what it does.

What are the values of the potentiometer that you use? I like that idea quite a bit.

You asked, "What are the values of the potentiometer that you use? I like that idea quite a bit."

Back in 2016, I tried a fixed output resistor of abut 2,200 ohms, but it set a code and I didn't have a scanner at the time to read the fooled temperature. So, I just bought a variable resistor and installed it (trial and error) and it worked. Later I purchased an OBDLink and dialed in the temperature of 143°.

It is easy to make the modification - just buy a couple of Deutsch 2-pin connectors with pigtails from Amazon for the wiring.

• John

Here are @Mopar1973Man 's observations.

Edited May 19May 19 by Tractorman