Engine too hot message on a cold engine

After sitting all night in my driveway, I get an “ engine too hot “ message within seconds after starting.  The temperature guage shows the engine is cold. The truck runs fine other than the AC won’t stay on.

2012 Chevy Silverado, 6 cylinder, 35,000 miles.  Being in southern Illinois, it is going to be profoundly uncomfortable about July 4.

Well, John, obviously, you have a very hot driveway!
Or... perhaps there is a super volcano under your driveway, and nobody but your truck has noticed this yet...
Otherwise, you have a failed sensor on the motor.
Your A/c not staying on, which could be because it thinks your motor is overheating.
The easiest sensor to locate is the one that controls the gauge, but we know it is working properly.
A quick search turned up the CTS sensor as a known problem with Chevy motors.
Either the sensor itself or the wiring going to it is where to look.

How are the fluid levels?  Ours does a warning like this if any of the fluids are low.  It often gets confused between oil, radiator, and the other ones.  It's good to check them all in case of cross wires warning light.

Hi r,

I thought it was a reach, but stranger things have happened.  Anyway, I checked the fluids, and they are fine.

To be clear, I am not talking about an Idiot Light.  A typed message appears on my dash.  

A quick run through google says the likely causes are a stuck thermostat, faulty ECT sensor, or 'electrical glitch'.  

Start with the easiest.  disconnect the negative battery terminal and leave sit for 15 minutes or so.  This will clear faults in the computer memory and hard boot the computer.  If the problem does not come back, you're golden.

If it does buy a new theromostat and install.  I have no idea what it should cost, but a thermostat used to be a $10 item.  They go bad over the years.

If that still does not fix the issue, you need to run a scan for OBI codes to narrow the electrical sensor that is twitchy.  If you are sure there are no actually over temp issues, you can just tolerate the false positives, but that can be annoying.

Also check (Fuses 12, 13, and 42 in the under-hood fuse box) that protect the cooling fans behind the radiator.  Quick and no cost to eliminate the possiblity of a gremlin there.

Next check your wires to the fans for any short, bare spot, or damage.  

My guess is you have a computer that is getting a false read, either from a software glitch or a a bad ECT sensor.  Let us know if we can help trouble shoot further.

It's not uncommon for the dash temperature and the ECU temperature to come from different sensors. My bet is the ECU-feeding temp sensor has died.

That's what it said on line, a message, not an idiot light.
Seemed like a common problem, easy enough to change.
https://www.youtube.com/watch?v=A2yVo9qfrzg