Spurious "Engine Hot, A/C Off" message

[gootchie]

I drive a 2007 Equinox LT, 156k on the odometer. Last week I got to work and noticed on my message center "Engine Hot, A/C Off". My coolant fans were both running full blast and my temp gauge had bottomed out, but nothing else seemed amiss. After sitting a couple hours in 36 degree weather, I came out on my break and checked the coolant tank, which was a little low (I flushed the heater core a couple weeks ago, and might not have topped off with enough coolant). I topped off the tank, then started the car and immediately got the same message, both fans blaring, so I knew it really wasn't an overheating issue. On the way home from work the message disappeared, and the temp gauge went back to its normal zone (slightly less than halfway). BTW the heater works fine too.

Obviously this is a sensor problem somewhere, but exactly which one could it be? Engine/coolant temp sensor? Could the thermostat be involved as well? Is this a common problem for this model Equinox? Just bought the car used last month, so don't know about its prior history.

[Stealthee]

Most likely the coolant temp sensor. When it fails the ECU thinks the engine is hot so it goes into a safe mode. Experienced this on a few GMs.

[Tech II]

Did you check for any codes?

And what was the reason for flushing the core?

Sounds like you have an air pocket....

[Stealthee]

In my experience it doesn't throw any codes. It's almost definitely the sensor or the sensor harness. When it happened to me one time I literally unplugged the harness and reseated it andvthey gauge cane back to life and the a.c. started functioning.

[gootchie]

Is the coolant temp sensor the one right below where the thermostat is housed?

[gootchie]

Update: Message popped up again one morning, and was soon followed by a check engine light with the code P0128 (thermostat). Since the thermostat seemed to be working fine (plenty of heat, reaching normal temp in a reasonable amount of time), I bet on the coolant temp sensor and replaced it. A week later, same problem occurs. Problem will either go away on its own by itself (message disappears, temp gauge starts reading normal), or a battery reset (removing negative cable) will clear it out. Works for a few days, then bam! happens again. Obviously something in the electrical/sensor system is triggering the failsafe mode, but I have no idea. Thermostat after all? Air in coolant? (I've read that might create a problem) Other than the aforementioned, everything seems to run fine. Any other ideas?

[Stealthee]

If you bought a cheap sensor you may have gotten a dud out of the box. It happens a l ot.

[brcidd]

Also, might be a nearly broken wire near the plug on the wiring harness- seen that a few times....Do the wiggle tug pull test...

[Tech II]

9 out of 10 times it's the thermostat.........

The code sets because of the amount of time it takes for the vehicle to get to normal operating temp......if the time is too long or does not reach the set temp, then the PCM turns the CE light on.....this happens because the therm is slightly open and allows too much flow through it....

Yes you will feel heat, and think the thermostat is ok.......vehicle is just not getting to normal temp on time, or it drops below this set temp while driving down the road, and does not get back to the set temp in a certain amount of time....

When ever I get one of these codes, I attach my scan tool, and let the vehicle idle until reaching normal operating temp, 190F+......

Then I go down the highway, and observe coolant temp data......if you see coolant temp dropping below 180F or more, replace the thermostat and clear the code...this will happen because the airflow through the radiator will cool down the coolant because of the bad therm.......stop and idle the car and it will eventually get back up to temp.....replace the thermostat....