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....