Engine Hot A/c Turned Off Code - Not Really Hot

[Hoodman]

Unfortunately the gremlin came back for about 5 minutes while driving to work. I did have my Verus all hooked up and ready. I was able to see the ECM was reading the ECT at 172 but as soon as I switched to the BCM the fault disappeared. Coincidence? No idea yet as that little &%$@* gremlin has not showed its ugly head again. I will follow up when it does.

[cody.meier]

I changed thermostat but didn't help. I figured it had to be electrical being that reseting the computer helped temporarily. So heres what I found- the wire harness that connects to the temp sensor,(drivers side behind alternator on my truck) the wire loom rotted off exposing all the little wires inside which rubbed on various engine components exposing bare wires and ultimately shorting out. It was very tedious trying to tape each wire but i managed to get it done and now its been good so far. Not saying this is the case with evryone with this problem but somthing else to consider while battling this "engine hot a/c off" problem.

 

BTW if my engine is hot that dont mean i want to be hot too leave my a/c alone

[NicholasYukon]

Got this warning on my dash, caused major "code" problems.  Turned out to be a simple thermostat thar needed replacing (mine was stuck open)  I would recommend doing that FIRST.  cheap and simple first fix. 

[Firebird21]

 I’ve had this problem for the last month. It started out by pegging the temp gauge and the classic warning coming on the dash.  Then the gauge just started dropping to zero and finally just staying at zero with the “engine hot” warning  still showing up even at a cold start-up.  Warm starts were becoming difficult, the cooling fans were on high at all times, gas mileage dropped, and it would not idle well as a result of the false information from the sensor.  The scan tool was reading 302 even though the temperature gage was at 0. 

 

 I found that the main harness was pierced by a stud on the driver side valve cover and had severed the yellow wire for the temp sensor in that harness.  This short also fried the brand new temp sensor I had put in earlier in a failed attempt to try and solve the problem.  I fixed the wire and put the old temp sensor back in and so far it’s working fine. 

[Jake Lake]

Same error issue for me. I fixed it. Open the rad to fill the coolant, don't just fill the resivoir. 

[jun]

On 1/2/2016 at 8:37 AM, fardanoh said:

I Have the GMC Sierra 3500 HD with a Vortec 6.0L . I've faced this problem well over a year now, and i only encounter its appearance after it rains, while in summer the engine works perfectly. i knew that the problem is back only from the temp gauge going lower to 90 degrees when its normally 100 (Celsius because I'm in Dubai) but i know the normal engine temp is 100. I've changed the thermostat earlier but the problem wasn't fixed, i cleaned out the battery wires after it then the problem was fixed for well over 9 months. And now the problem is back and its taunting me and really really pissing me off. Please HELP me because its my daily driver truck and i just wanna get over with this ****** and get it fixed. One trick i keep doing when this appears is that i disconnect the Battery wires and reconnecting again then the problem is fixed for a few hours, then its back again. The temp here in Dubai is over 40 degrees Celsius and i always boil while driving, Hell i even had to do the battery trick even when i was on a date. TWICE for gods sake, she never called again....

did u ever get this fixed? i have the same problem it started 6 months ago. i replaced my ect sensor & connector, and also rewired it directly to the ecm. my car is a 2009 suburban

[Dino Gravessi]

ISSUE:

There's a LOT of information on the internet about the "Engine Hot / AC turned off" message that scares everyone when it pops up the first time.  If the warning displays and the engine is not hot (one radiator hose kinda hot but the other is cold or barely warm) it's because the engine has not gotten up to operating temp in a set amount of time, usually around ten minute.  Sometimes the warning will be accompanied by a P0128 code,  “Coolant Thermostat Temperature Below Regulating Temperature”.  This is proof that it's not hot but actually too cold.  The issue occurs more often when the ambient temp is colder (winter).

 

SOLUTION:

You MUST have a 195deg thermostat in the system.  That's it.  The valve will stay closed longer and allow the engine to warm up to operating temp and you won't get a warning.

 

HEY GM!

The fact that there isn't a warning message for "Engine too cold" and instead "Engine Hot / AC turned off" gets used instead is completely unacceptable.  As an engineer I would be embarrassed to be part of the team who designed this system.