07 Tahoe engine hot ac turned off

[Dukenukemx]

So this problem has been happening for a while and I can't figure out why. First I changed the thermostat and it still happens. I changed the temperature sensor on the engine, and it still happens. I changed the wire going to the temp sensor and it still happens. Weird thing is that when I hook up my OBD2 reader it shows the engine running at 180F but the dash gauge is at 160F, which I assume is the lowest it can go. The message will go away at some point, but it will reappear again as well. I need help as to what the cause of the problem is.

 

[Big Mama]

Welcome from Virginia. So the gauge in the truck shows hot only when AC is off? Get a cheap infrared thermometer to see what it really is before adding more parts.

 

[Dukenukemx]

Welcome from Virginia. So the gauge in the truck shows hot only when AC is off? Get a cheap infrared thermometer to see what it really is before adding more parts.

The message means you can't turn on the AC when the engine is hot, but the engine is not hot. The fans are working constantly and I used a inferred thermometer on the engine and it's certainly not hot. Before I changed the temp sensor and wire, my OBD2 reader did show the engine running at like 120F, and after I changed it the issue went away for a while. It came back and when I read the OBD2 engine temp it shows 180F. Do I have air maybe in the coolant? Is there a way to bleed air out?

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics, please.

You already have one suggestion from our knowledgeable folks, and others will chime in.

 

[2011SSVTahoe]

When your engine thinks it is hot. Does your heater blow hot air. If it does not then you are low on coolant. 2 things I did was flush the engine and radiator and run cleaner thru it. If you have scale buildup in the head cooling passages it would mean real problems. Also, I cleaned the radiator externally too. Spraying water thru it from back to front to get the dirt and bugs out. When you add new antifreeze make sure to use distilled water, not tap water.

 

[Dukenukemx]

When your engine thinks it is hot. Does your heater blow hot air. If it does not then you are low on coolant. 2 things I did was flush the engine and radiator and run cleaner thru it. If you have scale buildup in the head cooling passages it would mean real problems. Also, I cleaned the radiator externally too. Spraying water thru it from back to front to get the dirt and bugs out. When you add new antifreeze make sure to use distilled water, not tap water.

It blows hot air. The radiator is brand new. The problem is gone now but who knows for how long.

 

[Tozan]

I am having the same problem with my 2011.

Dash reads "Engine hot AC turned off."
The temp gauge will not be registering anything
but, my OBD2 gauge will be reading in the normal temp range.

The code is PO128 Engine coolant temperature below thermostat regulating temperature.

If I clear the codes the warning goes away and the temp gauge in the dash will start working again.

This started after I replaced radiator all hoses and T-stat . It does not happen all the time.

 

[Big Mama]

You may have some air trapped in there.

 

[Tozan]

You may have some air trapped in there.

Not to likely since I have been on a lot of off road runs since filling it up a month ago. Plus with my system there are no high spots that do not self bleed themselves when it is filled up.

 

[Tozan]

I wonder if my (our) new radiators are working to well and it is taking too long for the motor to warm up... But, this does not really make much sense since the new radiator does not come into play until the T-stat starts opening up...

The PO128 "Engine coolant temperature below thermostat regulating temperature." sounds like it is not getting warm enough for the T-stat to do it's job...

It is also interesting when the code is "cleared" the dash temp gauge starts working again.

Still waiting on some of the experts here....

 

[HD_LS]

You are on to something there, with the radiators. Struggled with the hot, AC off bs for a while. I made a number of cooling system improvements at the same time, so it took a while to figure it out. But I think I have it solved on my machine. Source of the problem: Aftermarket radiator, with no flow restriction orifice in the small radiator hose connection, that goes to the surge tank. Coolant was flowing at a good rate from that top fitting into the surge tank, and if you look at the cooling flow circuit, this flow bypasses the thermostat. So it is essentially the same as having your thermostat half open all the time. I put a restriction in the hose, and have not seen the issue since then. Now why the "too smart for it's own good" ECM software is also programmed to interpret this slower than expected engine warm up rate as an overheat condition, is anyone's guess.

 

[adventurenali92]

You are on to something there, with the radiators. Struggled with the hot, AC off bs for a while. I made a number of cooling system improvements at the same time, so it took a while to figure it out. But I think I have it solved on my machine. Source of the problem: Aftermarket radiator, with no flow restriction orifice in the small radiator hose connection, that goes to the surge tank. Coolant was flowing at a good rate from that top fitting into the surge tank, and if you look at the cooling flow circuit, this flow bypasses the thermostat. So it is essentially the same as having your thermostat half open all the time. I put a restriction in the hose, and have not seen the issue since then. Now why the "too smart for it's own good" ECM software is also programmed to interpret this slower than expected engine warm up rate as an overheat condition, is anyone's guess.

This is correct. I just went through this scenario in replacing the radiator on my 2006 as well. I had read several threads where guys had replaced the radiator and the truck would not get up to operating temperatures. The “engine hot” but is new information. But they couldn’t figure out why the truck was not getting up to operating temp. And as you stated on the OEM radiator there is a small restriction piece in the top line that routes coolant to the surge tank. I was seriously concerned about how to resolve this if my new radiator didn’t have the correct piece installed. I lucked out and the aftermarket radiator I got from 1800radiator.com had the correct restrictor in place.
Edit: hard to see in the photo but that little restriction almost looks like a little washer installed inside the piping that connects to the surge tank line:

 

[Tozan]

Great I will check that out. That certainly sounds plausible If needed I could add an insert into the hose..

 

[OR VietVet]

Great I will check that out. That certainly sounds plausible If needed I could add an insert into the hose..

You can also just use a small hose clamp and squeeze the hose down a bit to restrict flow as well and see what happens.

 

[Dukenukemx]

I think the problem has been solved as I changed the temp sensor again, with a new thermostat again, and flushed the coolant... again. So far nothing wrong.

 

[Tozan]

You can also just use a small hose clamp and squeeze the hose down a bit to restrict flow as well and see what happens.

I used a C-clamp on the hose to restrict it, so far it seems to be working. So my next step is to determine how large of a hole in the restriction will be needed. Can anyone measure the ID of the stock fitting?

What is the main reason for this hose does it just need to vent air out of the radiator?

 

[Tozan]

So far the clamp idea is working great it has not happened since restricting the water flow in the top tank hose.

 

[kbuskill]

So far the clamp idea is working great it has not happened since restricting the water flow in the top tank hose.

Just had this happen to me this evening... driving home from church and the "Engine Hot, A/C Turned Off" message came on and the temperature gauge was sitting at the bottom (160°) but the OBD2 data was showing 142°. The truck was clearly not overheating and the coolant level was fine.

I just swapped to the Cold Case radiator last Saturday. Looks like I will be figuring out a restrictor for the upper surge tank hose.

 

[OR VietVet]

Just had this happen to me this evening... driving home from church and the "Engine Hot, A/C Turned Off" message came on and the temperature gauge was sitting at the bottom (160°) but the OBD2 data was showing 142°. The truck was clearly not overheating and the coolant level was fine.

I just swapped to the Cold Case radiator last Saturday. Looks like I will be figuring out a restrictor for the upper surge tank hose.

Small hose clamp and cinch down a little to create the restriction. High Tech!

 

[kbuskill]

Small hose clamp and cinch down a little to create the restriction. High Tech!

I think I am going to have a closer look at the old radiator and see what size hole it has up inside the radiator and then figure out which route I want to take.

I thought about having a buddy of mine tig weld an aluminum "washer" over the nipple.

It wouldn't need to be welded all the way around, just tacked in place, because the hose would slip over it and be clamped.

I will probably figure out something easier though.

A ball valve in line would be adjustable.