Overheats cooling fans do not come on

Welcome to 2CarPros.

I'm not totally understanding what you are saying, " Here's my issue: the cooling fans don't come on when the A/C is on cooling fans on high come on when regular heat is on cooling fans on low come on GM says that's normal so everything is working as it should computer says everything up to temperature everything's perfect everything's working perfect."

They don't come on when the AC is on or they come on high when the AC is on and low when the heat is on?

I attached two pics of the cooling fan circuit for you to review. I had to cut the schematic in half so it would be readable. I did overlap it so you can follow it.

Let me know exactly what is going on.

Take care,
Joe

Welcome back:

What is interesting to me is the fans are on low with the heater on. That shouldn't be unless you are running the defroster. Okay, I have attached several pics below related to the system. I start at the pcm / ect send signal. Voltage is to travel through the yellow wire to the ect. Based on engine temperature, resistance changes in the sensor and is allowed to travel to the low reference. From there, power is sent to the fan relays based on need. Interestingly, there is a splice in the wiring that I'm questioning. Also, the term "low reference" is referring to ground. What I need you to do is check for power first at the ect. If there is power, I need you to find the splice in the harness as indicated in the schematics and confirm there isn't an issue with corrosion or connection in any way. If it is good, then I need you to check continuity between the ect orange/black wire and where it plugs into the pcm.

If that all checks, and there is power to the signal send to the yellow wire on the ect, then you need to disconnect the PCM, inspect the pin for low reference (orange / black wire) in the harness for corrosion or if it is pushed in and not making contact. If it is good, check continuity for ground at the low reference pin in the PCM. If there is ground move to the next step.

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Once we know power is making it all the way through the system to the low reference, then we have to check for power out to the fan relays. If you refer to the pics I attached first, you will see the pins and wire colors. Now, this has to be done when the engine is hot and the fans should be on, so be careful. If there is no power out going to the relays, suspect a bad PCM.

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Here are the pics. Don't laugh at the arrows. I had to go across several pages for you to see everything and I made some really sad arrows to follow.

I realize this is a lot, but since they won't run based on the ECT sensor's request, something in this has failed. Please keep in mind, it could be something as simple as a loose connection at the PCM or even corrosion or a pulled pin in the harness. However, I have a feeling that you may find an issue at the splice indicated.

Let me know what you find, if you have questions, or need help. One last thing. Picture 2 is a continuation of the bottom portion of pic 1. I just wanted you to know where I started and couldn't fit everything into one picture and make it readable. After pic 2, everything will follow a natural order.

I have one last really stupid question. Are you certain the ECT is the correct one and although it's new, it is good?

Take care,
Joe