About a year ago I got an "Engine Hot/AC Off" light on my 2007 3.9 Impala. It went off and didn't come on for a long time. About 3 months ago I got a check engine light. Had it checked at Advance and they said it meant my coolant temp was low. They said the fix was a new thermostat. The light went off and I didn't worry about it. It would come on and go off every once in awhile for a month. Then the Engine Hot warning came on and the dash temp gauge bottomed out. The cooling fans ran constantly and there was no AC. I changed the thermostat but the light stayed on. I used a computer to reset the code. The fans went off and the AC started working for 10 days. Then I got the Engine Hot/ AC Off light. Rechecked the thermostat and moved on coolant temperature sensor. When I went to remove the sensor, the plug was brittle from the heat and it fell apart. The plug end of the sensor was also brittle and broke off. I changed the sensor and went to a junk yard and cut the plug off a 3.5 Impala. I spliced it onto my car and plugged it in. I disconnected the battery for 30 seconds and haven't had the problem since. I brittle plug would explain why the problem would come and go.

 

Hopefully your solution works long term.
Swapping thermostat and/or temp sensor is about the only thing diy folks can do.
What the folks at Advance did not tell you is that the error code actually says the coolant temp is 'not rising fast enough' to suit the ECM. Seems to be some sort of 'logic' decision made by the cars control module. What is illogical is the decision to declare the engine is 'HOT' while still at normal temp.
I believe in all cases the apparent loss of gauge temp is the sensor output being turned off by the ECM..along with the radiator fans turned on.
Functionality always returns as soon as the error code is reset....if only for a short while.
Regards,
Bill

 

I have had this problem recently and I've watched many of videos looked at many of forms and I finally figured it out. If you have already changed the temperature sensor and the thermostat make sure that you correctly fill your radiator fluid with Dexcool properly portioned with water half and half filled all the way to the rim turn your car on heat and let it run for 5 minutes and fill it again make sure that it is full and if this will solve your problem do not mix anything with Dexcool except water no green or you will have a bad day!

 

Seems to be across several models. Mine is intermittent. Lasts a couple cycles and then works right. Have done the usual...replaced thermostat, flushed radiator. But since it occurs at key on...I don't think it's mechanical. Getting to end of the rope with this ..need some insight

 

how exactly do you quickly disconnect the positve cable because there is certainly not easy access

 

I swear it’s not the thermostat. We’ve had our 2006 Impala in off & on over the last week THREE times to no avail. Started with car overheating to full steam/smoke in Walmart parking lot which was a cracked radiator. Picked up car & it overheated while idling and started steaming to a lesser level about 3 days later; replaced the water pump. Picked up & drove it about 20 mins and got warning ⚠️ “Engine Hot - A/C Off”. Our A/C hasn’t worked in months so that obviously wasn’t on. Towed to Firestone again & replaced thermostat this time. Picked up last night, drove home fine, drove 25 miles to work fine this AM, then got error msg AGAIN after it sitting in a parking lot for a good 8 hours in 40*F weather. 🙄 Called dealership who recommended checking error codes on computer & temp sensor if not already done. Got another appt tomorrow at Firestone.

 

saralyn.
welcome to this thread and sorry.
So far, you are the first to get a “Engine Hot - A/C Off” warning light due to the engine actually overheating.
The rest of us are still at a loss to identify a specific problem with coolant temp.
Going forward, it will be interesting to see what symptoms appear in your case.
The DIC warning is too misleading since it tries to alert you to a variety of potential OBD codes recorded in the cars computer.
The best advice given to me by the grownups on this thread is to first check the error codes. once they are resolved, the DIY warnings messages will go away.
In my case, i logged a "P0128" OBD error code which means the ECM had decided that the engine was not warming up as fast as it would like.....and still got the "ENGINE HOT" warning and dead temperature gage on the dash, despite the fact that the coolant temperature was fine.
so far all the fixes appear to be relatively subtle changes to a coolant system that seems to work fine.
for me, replacing the thermostat has resolved my error message for the last 2 years.
in other posts, some have had success flushing and replacing the coolant.
Others have identified potential problems with the temp sensor or its wiring and connectors.
All of the “fixes” appear to alter the temperature profile recorded by the control module which prompts certain OBD error codes and the totally illogical DIC message “ENGINE HOT/AC OFF”
The arrival of fall and cooler morning temperatures also seemsto be a factor in triggering the P0128 code. I assume that is because a lower initial coolant temp will delay temps reaching some predetermined value.
Again, find the specific OBD code your car is logging. Deal with that first and the DIC message will go away.
If you get p0128, simply changing thermostat, temp sensor and coolant is cheap and simple place to start.

good luck.

 

 

I’ve changed both the thermostat and the ect sensor and I’m still having this problem. It’s amazing this hasn’t been a recall. How many people need to have this issue?

 

Check to see which OBD codes may have been logged. The ENGINE HOT message doesn’t seem to identify a specific problem despite the specific wording.Regardless, fix the errors identified by OBD