Do some forum searches, a common issue, a failed thermostat assembly. Check engine light was most likely on with a code P0128.

 

1just had it checked this morning .from disconnecting the negative battery post . we not only cured the problem for the moment but also erased any codes . so its good thing but also a bad thing . so have to wait for it to happen again .

 

Pretty safe bet, it will happen again.

 

Yes, it will happen again. The coolant temperature sensor is the culprit. It's part of the thermostat housing. $167.00 at our local Advance. The unit is located under the intake manifold.

 

This isn’t quite right.


The coolant temperature sensor has not been shown to be a definite problem. Most people replace it because it’s not expensive and they’re elbow deep into the job and it’s right there. A “might as well” but not required.

The thermostat itself is the root cause. If you’re only going to do one part, that’s the one.

Also the temperature sensor is not part of the thermostat housing really. It sits in a valley below. If you want to go after the sensor you’ll need a crows foot 15mm.

There’s been a LOT of us that have gone through this if you search P0128. Many threads with LOTS of detailed help including all the part numbers you’ll need and some video links. Strongly recommended!!

 

Unless they changed the design in 2021, my 2018 thermostat & sensor were 2 separate parts going into very different locations. The thermostat hsg was in the valley of the engine & the sensor was near the rear bank & on the passenger side. I only replaced the thermostat & never had a code set since. YMMV.

 

I have a 2020 gmc Acadia and just went through the same issues. It was the thermostat that needed to be replaced.

 

Exactly what it was no issues since...

 

the thermostat was the problem . i'm not sure why gm decided that it was a bright idea to design the V - 6 were it is located . but a royal and costly repair for a thermostat . 6 hour repair on my 2021 Acadia . was just glad we had a extended warranty car only had 44,000 miles on it. after this and the fuel sending controller unit going at 39'000 mile .we be looking away from GM next time im in the market for a new car.