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Discussion Starter · #1 ·
Hey guys so my car reads Engine Hot AC Off with the Fans running 24/7 when that code is up.(The car is not overheating) but the temperature gauge drops to cold like all the way down No engine Light. Eventually it comes on. I Changed the Engine Coolant Sensor and thought that was the fix but it wasnt. The "Engine Hot AC Off" comes on when i put the heat on full blast then the message stays on. When i reset the battery it obviously tricks the computer for a little and runs normal without the message. Does anyone know a fix ?
 

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Thermostat stuck open. They do that. Lots of posts on here about that. Mine too did that very thing. Rubber gasket in the thermostat takes a crap and gets stuck in there holding it open. Can be a bit of a challenge to change but not all that bad. Word of advice though. Get an extra gasket for it when you buy it. They can be a bit fiddly to get back in and can get messed up or nicked. ( basically an O ring ).

Murphy's law.

If you have an extra you wont need it, if you don't you will.

Good luck.

Use the search function and find some posts on this subject. There are even some with some pictures of what to do and likely what you'll find. I think I have some on here somewhere but using my phone right now to comment and it's a PITA searching stuff like that.

Let us know and welcome to the forum.
 

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Discussion Starter · #3 · (Edited)
Could it still be the thermostat if it runs normal when i reset the computer by pulling the battery terminals off? Then eventually the message will come back after a few days...
 

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Discussion Starter · #4 ·
Thermostat stuck open. They do that. Lots of posts on here about that. Mine too did that very thing. Rubber gasket in the thermostat takes a crap and gets stuck in there holding it open. Can be a bit of a challenge to change but not all that bad. Word of advice though. Get an extra gasket for it when you buy it. They can be a bit fiddly to get back in and can get messed up or nicked. ( basically an O ring ).

Murphy's law.

If you have an extra you wont need it, if you don't you will.

Good luck.

Use the search function and find some posts on this subject. There are even some with some pictures of what to do and likely what you'll find. I think I have some on here somewhere but using my phone right now to comment and it's a PITA searching stuff like that.

Let us know and welcome to the forum.
Could it still be the thermostat if it runs normal when i reset the computer by pulling the battery terminals off? Then eventually the message will come back after a few days...
 

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Are you actually getting good heat from the heater ?
The thermostats are pretty common to fail on these guys. Not sure about reseting the readout and trying again.
I have no answer for you about that. Sorry.
 

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Discussion Starter · #6 ·
Are you actually getting good heat from the heater ?
The thermostats are pretty common to fail on these guys. Not sure about reseting the readout and trying again.
I have no answer for you about that. Sorry.
Yes the heat works fine when the message "Engine hot Ac Off" is NOT on. When the message is ON the heat isnt as strong. Windows stay foggy ,defrosters take longer to work.
 

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Makes sense as the air dryer is disabled with the AC off. I'm still leaning towards the thermostat, but ,,,,,,, resetting the readout is a factor I don't know.
Sorry.
 

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I had that problem my temperature hand will move up 1-2 bars then back down constantly. 2006 Impala 3.9L. Never paid it any attention to it until my mechanic pointed out that only one of my fans were working and it was pushing out air the other side was suppose to be doing. Running 2x it's speed. So what I had to do to fix that problem was:
A new thermostat housing unit & sensor, radiator fan, & water pump. One of those fixed it. (I really think water pump fixed it for good because that was the last installment that made me say ok good)

Good luck trying to fix. If you have a code that came from a scanner that helps alot.

Oh yeah my heating and stuff works now after the water pump was fixed. Defroster and all.
Most of the time the heat wouldn't work unless the car was in motion.
 

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Could it still be the thermostat if it runs normal when i reset the computer by pulling the battery terminals off? Then eventually the message will come back after a few days...
I would say yes. I just replaced the thermostat on my 08 that was doing the same thing as yours. I was clearing the code with my bluetooth OBD reader and it would stay off for a day or so.
 

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Discussion Starter · #10 ·
Could it still be the thermostat if it runs normal when i reset the computer by pulling the battery terminals off? Then eventually the message will come back after a few days...
I would say yes. I just replaced the thermostat on my 08 that was doing the same thing as yours. I was clearing the code with my bluetooth OBD reader and it would stay off for a day or so.
Ok thank you. Did you replace your coolant as well? Or used the same?
 

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That antifreeze, if original, which I suspect it is, should be changed out anyway.
It's 9 yrs old.

If you have a spill proof funnel for refilling that would be handy. Getting all the air out of the system can sometimes be a bit of a challenge.

Good luck and let us know how it goes.
 

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My 2008 Impala LT gets this condition, I get code P0128 - Coolant Temperature Below Thermostat Regulating Temperature. I have not yet replaced the thermostat, I don't plan on fiddling with it myself so am saving up to have it done. I do know that it's more likely to happen when outside temperature is less than 60 degrees. Clearly my thermostat is stuck open when the Engine Hot A/C Off appears because the car will only get heat after driving highway speed for several miles. Will heat up to normal in city driving but engine temp will drop on the Interstate. Cold air flowing through radiator and stuck-open thermostat cools too much LOL. After reading the other posts I'm convinced my thermostat sticks but only intermittently. A real pain in cold weather because it's most likely to stick below freezing it appears. The P0128 sold me on that being the problem. I use a Bluetooth OBDII tool and just reset it with my phone when Engine Hot A/C Off comes up. Doesn't help the car get heat but at least I can see the temperature gauge... LOL
 

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Discussion Starter · #13 ·
My 2008 Impala LT gets this condition, I get code P0128 - Coolant Temperature Below Thermostat Regulating Temperature. I have not yet replaced the thermostat, I don't plan on fiddling with it myself so am saving up to have it done. I do know that it's more likely to happen when outside temperature is less than 60 degrees. Clearly my thermostat is stuck open when the Engine Hot A/C Off appears because the car will only get heat after driving highway speed for several miles. Will heat up to normal in city driving but engine temp will drop on the Interstate. Cold air flowing through radiator and stuck-open thermostat cools too much LOL. After reading the other posts I'm convinced my thermostat sticks but only intermittently. A real pain in cold weather because it's most likely to stick below freezing it appears. The P0128 sold me on that being the problem. I use a Bluetooth OBDII tool and just reset it with my phone when Engine Hot A/C Off comes up. Doesn't help the car get heat but at least I can see the temperature gauge... LOL
You are the type of people i like ! Haha! Sound just like me. Ill be changing my thermostat today. Hope for the best!
 

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Discussion Starter · #14 ·
My 2008 Impala LT gets this condition, I get code P0128 - Coolant Temperature Below Thermostat Regulating Temperature. I have not yet replaced the thermostat, I don't plan on fiddling with it myself so am saving up to have it done. I do know that it's more likely to happen when outside temperature is less than 60 degrees. Clearly my thermostat is stuck open when the Engine Hot A/C Off appears because the car will only get heat after driving highway speed for several miles. Will heat up to normal in city driving but engine temp will drop on the Interstate. Cold air flowing through radiator and stuck-open thermostat cools too much LOL. After reading the other posts I'm convinced my thermostat sticks but only intermittently. A real pain in cold weather because it's most likely to stick below freezing it appears. The P0128 sold me on that being the problem. I use a Bluetooth OBDII tool and just reset it with my phone when Engine Hot A/C Off comes up. Doesn't help the car get heat but at least I can see the temperature gauge... LOL
You are the type of people i like ! Haha! Sound just like me. Ill be changing my thermostat today. Hope for the best!
UPDATE- Thermostats changed. Coolant flushed.

So far so good.

My rear defroster now works since i changed the thermostat. So I'm hoping that was the fix!
 

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UPDATE- Thermostats changed. Coolant flushed.

So far so good.

My rear defroster now works since i changed the thermostat. So I'm hoping that was the fix!

That's awesome! I really hope that is the fix! I have yet to change out my thermostat, I'm hesitant to do it myself because of lack of tools where I live and it being with the lower radiator hose.. Was it hard to replace? Let me know if it solved the problem, I'll be next! Dealer wants $200 to change it so DIY would be WAY better!
 

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Impala Engine hot, A/C off

There are two typical issues that cause this message to appear:
1. The ECT sensor (or wiring) is open or otherwise defective, or
2. The inner seal on the thermostat is deformed, allowing coolant to bleed through when the thermostat is closed. This causes the car to warm up too slowly, and the computer throws an incorrect flag: "Engine hot, A/C off".

You should check/fix these issues in the following sequence:
1. Use a scan tool to clear the codes. If the ECTS or wiring is open, the "Engine hot, A/C off" message should return immediately. If so, replace the ECTS or check the sensor wiring for defects. However, if the code does not return immediately, this does not automatically mean the sensor is OK. The sensor or the wiring could be intermittent. But you should move to the next step first.
2. Check how long it takes for the car to warm up. If it seems to take longer than normal, this is an indication that the thermostat is experiencing bleed-through. If so, replace the thermostat. (This is much easier than replacing the ECT sensor.) Once you get the thermostat out, inspect the inner seal. If it has twisted out of position, this was your problem. Replace the thermostat, and use a scan tool to clear the codes.

Changing the thermostat is fairly easy, and it may be a pretty old piece of equipment anyway. I lost about a gallon of coolant, but this fixed the problem on my 09 Impala with 155K miles.
 
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