[KRoss0208]

It's probably not even the thermostat. A bunch of people with the 2017 Acadia Denali have experienced that same exact symptoms as have I. It seems that if you unplug the Negative Battery Terminal that it clears these errors and everything starts working normally again. It worked for me.

I almost dropped $1400 to have the thermostat replaced. Then I did the battery terminal thing and cleared the errors. If it was the thermostat like I thought then the issue would have came right back as I have been driving it all over town and it's been in the 90s here in Arizona already. Been a week now and everything is working fine.

I think this is just another software gremlin with the 2017 Denali.

Interesting, I literally just got our 2019 back from the dealership (Friday) for having them replace the sensor. Thought it was good to go until I started driving home this afternoon and got the steering is reduced and realized the gauge isnt moving again. I am going to have my husband try your battery idea and see if it works. Not sure I want to go pay to have the thermostat done - when the gauge works its fine, hence why I thought it was just a sensor issue.

 

[ILl Awm An]

Mike, I think you just saved me a whole weekend (full of cursing) and $150 parts to replace the thermostat and temp sensor myself, or $700 at a shop, or $1300 at my local GMC dealer. My '17 Denali had all the symptoms-- steering assist error, no coolant temp, fan running full blast, and no AC. I was about to order the parts, had already watched a couple YouTube vidoes to figure out if I could do it myself or not. Saw your post and thought, what the hell, I'll give it a shot.

So, I go to loosen the negative battery terminal... but it's already loose. Dealer replaced the battery three months ago, and apparently didn't adequately tighten the terminal nut. BUT! It didn't work right away-- it still gave me the error, no AC, etc., and I was still bummed. After about two cycles of 10-15 miles driving, engine off, start again, BOOM, the software must have finally reset. Temp gauge working, AC blasting cold, no steering assist error.

Anyway, thank you, Mike!!!

TL;DR: CHECK YOUR BATTERY CONNECTIONS FIRST! THESE SYMPTOMS CAN BE PRODUCED BY A LOOSE TERMINAL CONNECTION!

Update: Unfortunately, the thermostat symptoms are back... but intermittently. Battery connection is (now) tight. So, might be the sensor or the thermostat after all. Local non-dealer, chain tire and auto center quoted $1166 for thermostat, sensor, and coolant flush. Woof.

 

[tmcbee1228]

Having the same issues with my 2017 Acadia SLT. No steering issues but temp Guage drops to 160 and ac quits working. Put an analyzer on it says it's the coolant sensor. Bought one but have no idea of the location. 3.6L vvt. Looking for help

 

[JayTee2019]

Having the same issues with my 2017 Acadia SLT. No steering issues but temp Guage drops to 160 and ac quits working. Put an analyzer on it says it's the coolant sensor. Bought one but have no idea of the location. 3.6L vvt. Looking for help

As I recall, the engine coolant sensor . . or at least one of them .. . is located next to the thermostat housing/outlet ( Yellow Arrow in picture ) on top / center of the engine down in the front of the "valley" under the intake manifold.
It would be on the passenger side of the engine.
See the picture below and reference the included Youtube of the replacement procedure that helps greatly.
The second Youtube shows replacing the coolant sensor on the same V6 in a Camaro IIRC. . . and may help in how to release the electrical connector to it.
Either way, it seems you will have to remove the Intake Manifold.

Coolant Sensor Remove/Replace

 

[2019AcadiaDenali]

I would recommend resetting the computer by disconnecting the negative battery terminal, has worked 3 times for me so far. Will be contacting GMC as this is unacceptable but at least gets it working again.

 

[etomlinsonit]

Had the same issue, no A/C, Power Steering Assist Reduced/Disabled notification, Fan running all the time, Engine Temp at 0, and P0128 Code.
Had to go to the dealer to get the following parts
Manifold Gaskets x6 Part# 12648665
O-rings for the 2 return lines x2 Part#12648547
Thermostat assembly and water pipe Part# 12678779
Engine Temperature Sensor (might as well replace this $12 part at the same time) *This one you can get anywhere Part# TX281
Cost $276
If I had brought it to a shop - $1627.00
Took roughly 3-4hrs to complete
Best videos for walk through

I had to unseat the ground on the battery and reseat (reset the system) - Problems resolved.

 

[JayTee2019]

Had the same issue, no A/C, Power Steering Assist Reduced/Disabled notification, Fan running all the time, Engine Temp at 0, and P0128 Code.
Had to go to the dealer to get the following parts
Manifold Gaskets x6 Part# 12648665
O-rings for the 2 return lines x2 Part#12648547
Thermostat assembly and water pipe Part# 12678779
Engine Temperature Sensor (might as well replace this $12 part at the same time) *This one you can get anywhere Part# TX281
Cost $276
If I had brought it to a shop - $1627.00
Took roughly 3-4hrs to complete
Best videos for walk through

I had to unseat the ground on the battery and reseat (reset the system) - Problems resolved.

Thanks for posting . .. and . . yes, that is about the best video that I found on Youtube for this repair.
It has been posted on a couple other threads regarding this issue, but good to have it for more access.

Thank you also for supplying the part number for ALL the parts needed.

For anyone that is handy with tools, it is a great money saver and not too difficult. Just make sure to cover the intake piorts while doing the repair so that nothing can drop down into a cylinder .

 

[cchagoya7337]

Interesting, I literally just got our 2019 back from the dealership (Friday) for having them replace the sensor. Thought it was good to go until I started driving home this afternoon and got the steering is reduced and realized the gauge isnt moving again. I am going to have my husband try your battery idea and see if it works. Not sure I want to go pay to have the thermostat done - when the gauge works its fine, hence why I thought it was just a sensor issue.

It's probably not even the thermostat. A bunch of people with the 2017 Acadia Denali have experienced that same exact symptoms as have I. It seems that if you unplug the Negative Battery Terminal that it clears these errors and everything starts working normally again. It worked for me.

I almost dropped $1400 to have the thermostat replaced. Then I did the battery terminal thing and cleared the errors. If it was the thermostat like I thought then the issue would have came right back as I have been driving it all over town and it's been in the 90s here in Arizona already. Been a week now and everything is working fine.

I think this is just another software gremlin with the 2017 Denali.

has the issue returned? I have done the disconnecting the negative terminal thing. Went away for about a week. Now it’s back. Any update?

 

[Ty Williams]

Yes. I’m guessing that’s mainly for the labor. Just took it to pep boys and it’s reading that same code. Wondering if I should just find a garage and not deal with the dealership

Did you get it fixed? Did you use a garage or dealer? I'm facing the same issue and was curious about the cost to fix it.

 

[JayTee2019]

Did you get it fixed? Did you use a garage or dealer? I'm facing the same issue and was curious about the cost to fix it.

There are quite many of this problem reported here in the forum.

First, there is a tech bulletin that states this may be covered by GM. So check with some GM dealers or call GM Customer Service and ask how you may proceed since this seems to be a chronic issues with some GM vehicle Thermostats failing.

It's best to start looking at and calling repair shops that might do this properly. You may get a low cost quote, but if the techs are not competent or familiar with this kind of repair, other things may be damaged and show up afterwards.

If it happens to our Acadia, we will be taking it to a local GM repair department.

From what I have seen, it generally has cost between $1,100 and $1,800 to get the Thermostat and Engine Coolant Temperature sensor replaced that causes it.
The lowest cost, if i recall correctly, was about $900, but that was at an independent repair shop and I think the owner purchased the parts themselves before having it repaired.

As with any automotive repairs, it depends on the area you live in and what the cost of living may be among other things.

 

[ILl Awm An]

There are quite many of this problem reported here in the forum.

First, there is a tech bulletin that states this may be covered by GM. So check with some GM dealers or call GM Customer Service and ask how you may proceed since this seems to be a chronic issues with some GM vehicle Thermostats failing.

It's best to start looking at and calling repair shops that might do this properly. You may get a low cost quote, but if the techs are not competent or familiar with this kind of repair, other things may be damaged and show up afterwards.

If it happens to our Acadia, we will be taking it to a local GM repair department.

From what I have seen, it generally has cost between $1,100 and $1,800 to get the Thermostat and Engine Coolant Temperature sensor replaced that causes it.
The lowest cost, if i recall correctly, was about $900, but that was at an independent repair shop and I think the owner purchased the parts themselves before having it repaired.

As with any automotive repairs, it depends on the area you live in and what the cost of living may be among other things.

Super annoying that GM has a "tech bulletin" advising their techs how to properly diagnose this common "error"... but it's not a recall so they won't foot the bill for what is clearly a defect.

 

[ILl Awm An]

Thanks for posting . .. and . . yes, that is about the best video that I found on Youtube for this repair.
It has been posted on a couple other threads regarding this issue, but good to have it for more access.

Thank you also for supplying the part number for ALL the parts needed.

For anyone that is handy with tools, it is a great money saver and not too difficult. Just make sure to cover the intake piorts while doing the repair so that nothing can drop down into a cylinder .

My temperature sensor/thermostat issue has been coming and going since May. Error will be on for 3-5 days, then off for 2-3 weeks; repeat. Luckily I made it through most of the summer without it being an issue; it knocks out the AC but not the heat when it's not working. I've decided I'm going to dive in and try to fix this on my own, but admittedly this will be the most involved auto repair I've ever attempted. Happy to spend a couple hundred in parts and get some ratchet extensions to save a grand over the dealership. Parts look to be in stock and prices are down, I'm pricing everything out at $185 - $225 depending on GM parts retailer.

A couple questions, if you'll indulge me: Some of the videos mention the torque specs for some bolts, but not others. Is there a master list of torque specs? Also, you start by draining the coolant. Should I then do a coolant flush, or just refill with the 50-50 dexcool-water solution once everything's completed? My 2017 has 85k miles-- is that just the shelf life on this sensor? Seems like many are running into this problem below 100k miles.

Thanks for the assist, Acadia braintrust!

 

[JayTee2019]

My temperature sensor/thermostat issue has been coming and going since May. Error will be on for 3-5 days, then off for 2-3 weeks; repeat. Luckily I made it through most of the summer without it being an issue; it knocks out the AC but not the heat when it's not working. I've decided I'm going to dive in and try to fix this on my own, but admittedly this will be the most involved auto repair I've ever attempted. Happy to spend a couple hundred in parts and get some ratchet extensions to save a grand over the dealership. Parts look to be in stock and prices are down, I'm pricing everything out at $185 - $225 depending on GM parts retailer.

A couple questions, if you'll indulge me: Some of the videos mention the torque specs for some bolts, but not others. Is there a master list of torque specs? Also, you start by draining the coolant. Should I then do a coolant flush, or just refill with the 50-50 dexcool-water solution once everything's completed? My 2017 has 85k miles-- is that just the shelf life on this sensor? Seems like many are running into this problem below 100k miles.

Thanks for the assist, Acadia braintrust!

Good research on the parts . . and I agree the T-stat and sensor are both pain to replace and it is a puzzle why some fail with relative low miles and others after several years.

I am not aware of the torque specs, but one of the videos, IIRC , mention one or two of the bolts for the T-stat having a spec. I've done T-stats in the past and just tightened down to a snug point and then maybe a few degrees more.
The thing that seems to be fussy is to get new o-rings for the "water outlet" thing attached near the T-staf. Also, the fittings need care to unfasten to not damage how they work.
Also, care for the electrical connection to the coolant sensor. Those plastic keepers on the connectors need to be slid one way or another to release the connector.

I would just drain and fill the coolant but not use any chemical flush. Flush chemicals can leave residue or other agents that may contaminate the Dexcool 50/50.

Hope it goes well for you. That coolant sensor looks like tough to get a wrench on and also the pipe across the engine valley and "foam" that needs to be removed on the other end.

 

[pjfizzlebean]

YES! I did all of the above - replaced the thermostat myself, and all was good for a month. Then I got the P0128 code again. Luckily, I saw your post! It reoccurs, but only in hot, humid weather; it hasn't failed since Fall. I suspect it's either the ECM or a bad electrical connection. Anyway, thanks for the tip - it saved me a bunch of time/money.

 

[Ben L 92]

Okay so had this issue and read this thread, can confirm that I did the negative terminal removal for 10min this morning. It has fixed the issue for now and I'll update to let you know how long before and if it comes back. Just a heads up, make sure you have your remote near by it could set off the car alarm off when you reconnect it 😂

 

[garytexasdelta]

I had my local garage change my sensor with a GM sensor, and it was done in 1.5 hours whereas the dealer wanted to charge 4.5 hours. This didn't solve the issue, so I went to the dealership who gave me a special discount, and after testing the vehicle stated it was the thermostat. They quoted me $1280, but the parts accounted for $200 of that. My local garage purchased GM parts for much less, and will install these tomorrow. I am expecting a bill of 1/3 of the dealership. It has all the same issues as stated in this post.. .. fan running, no ac, power steering assist, gauge shuts down..all intermittent.

Thanks for posting your results. I just replaced the harness and left the old sensor for troubleshooting. This can be done by removing only the air box on top. When I metered the two wires in the old harness, I found an intermittent "open" in one of them when I moved the connector for the sensor.

 

[Danimal78]

I have a 2021 Acadia AT4 that has had this error 3 times and been at the dealership 3 times for it. Last time it was there for 2.5 weeks for them to change a sensor that was located under a fuel rail (or so they told me) apparently they pull the rail with a vacuum and it was stuck. The error message came back yesterday, but I'm still covered under the 36,000-mile warranty (I have 35,600 miles on it). I have zero faith in GM or their techs to actually fix it... such A pity because I do love the vehicle, guess I'll have to buy an extended warranty if I wanna keep it (I do have the ability to wrench but not the time). I wonder if this is happening with all GM vehicles or if it's strictly an Acadia issue??

 

[JayTee2019]

I have a 2021 Acadia AT4 that has had this error 3 times and been at the dealership 3 times for it. Last time it was there for 2.5 weeks for them to change a sensor that was located under a fuel rail (or so they told me) apparently they pull the rail with a vacuum and it was stuck. The error message came back yesterday, but I'm still covered under the 36,000-mile warranty (I have 35,600 miles on it). I have zero faith in GM or their techs to actually fix it... such A pity because I do love the vehicle, guess I'll have to buy an extended warranty if I wanna keep it (I do have the ability to wrench but not the time). I wonder if this is happening with all GM vehicles or if it's strictly an Acadia issue??

This P0128 code and indication of an ECT sensor and/or failing thermostat have been showing up on other GM vehicles like the Colorado/Canyon and Camaro cars that use the same 3.6L LGX engines and same symptoms.

However, on the trucks and Camaro car, the thermostat and sensor are not buried under the fuel rail and intake manifold so it is possible to change them a bit more easily . . . although still a tight fit.

That said, there is some indication that this may actually be some electrical connection failure. . (intermittent ?) or glitch in the way the ECU interprets coolant temperature in some circumstances.
Others say it is the thermostat that sometimes "sticks" open and causes the error and shut down of A/C and gauges to misread.

There are more than several of us, and dealer techs as well, that are at odds as to what really is occurring.
Dealer techs these days have to follow GM recommended sequence of repairs on warranty issues like this. They have to replace things in steps according to the SIP I believe it is called.
That said. . . besides that and sometimes new and inexperienced repair employees, I too have pause to take any of my 3 GM vehicles in for repairs. I've had several times when things went amiss in the past 10 to 12 years and before that always had good faith and few if any issues with my GM vehicles nor repair technician quality.

I think a good deal of it has to do with the complexity of interlinked operation between the various modules and sensors in these newer vehicles and the communication network that they all communicate over to each other. It's not unlike the internet or at least the LAN you may have at home for your various computers, tablets, and other devices.

I too can "wrench" and have for many years. However, I do not enjoy doing repairs in a cold unheated garage where hands fingers and my bones don't work the best.
I well remember the days of lying on my back under a car or truck and having road salt melt water dripping on hands and face while I busted a knuckle doing one thing or another.
I don't know how many times I was working and didn't know why the wrench was getting slippery and difficult to hold on to. . . . only to find the last slip of the wrench caused a gash or cut.
I don't care to do that anymore. Especially after getting older. Yet I cringe thinking about who is working on my vehicle and what they may not be doing correctly.

 

[goodboyjdpr]

Hice. Reemplacé mi termostato hace aproximadamente un mes y mis problemas desaparecieron. Esto parece haberlo arreglado. Reemplazar el termostato fue una tarea difícil y me tomó alrededor de 4 horas, pero puedes hacerlo. Debe quitar los elementos de la parte superior del motor, como la entrada de aire e incluso el riel de combustible, luego el termostato está debajo de eso. El termostato cuesta alrededor de $ 150 porque obtienes la carcasa y la tubería con él.
[/CITA]
donde conseguiste el termostato?

 

[Acadianagain]

This P0128 code and indication of an ECT sensor and/or failing thermostat have been showing up on other GM vehicles like the Colorado/Canyon and Camaro cars that use the same 3.6L LGX engines and same symptoms.

However, on the trucks and Camaro car, the thermostat and sensor are not buried under the fuel rail and intake manifold so it is possible to change them a bit more easily . . . although still a tight fit.

That said, there is some indication that this may actually be some electrical connection failure. . (intermittent ?) or glitch in the way the ECU interprets coolant temperature in some circumstances.
Others say it is the thermostat that sometimes "sticks" open and causes the error and shut down of A/C and gauges to misread.

There are more than several of us, and dealer techs as well, that are at odds as to what really is occurring.
Dealer techs these days have to follow GM recommended sequence of repairs on warranty issues like this. They have to replace things in steps according to the SIP I believe it is called.
That said. . . besides that and sometimes new and inexperienced repair employees, I too have pause to take any of my 3 GM vehicles in for repairs. I've had several times when things went amiss in the past 10 to 12 years and before that always had good faith and few if any issues with my GM vehicles nor repair technician quality.

I think a good deal of it has to do with the complexity of interlinked operation between the various modules and sensors in these newer vehicles and the communication network that they all communicate over to each other. It's not unlike the internet or at least the LAN you may have at home for your various computers, tablets, and other devices.

I too can "wrench" and have for many years. However, I do not enjoy doing repairs in a cold unheated garage where hands fingers and my bones don't work the best.
I well remember the days of lying on my back under a car or truck and having road salt melt water dripping on hands and face while I busted a knuckle doing one thing or another.
I don't know how many times I was working and didn't know why the wrench was getting slippery and difficult to hold on to. . . . only to find the last slip of the wrench caused a gash or cut.
I don't care to do that anymore. Especially after getting older. Yet I cringe thinking about who is working on my vehicle and what they may not be doing correctly.

I can surely relate to the frustration all have expressed here and hope to find a real fix to this annoying problem that doesn’t reward the makers of said problem.
Same situation with our ‘19 Acadia receives a bad intermittent temp signal that causes an ECM error that SHOULD self correct if programming is done correctly. One can wonder if errors are programmed correctly 🤔
Nothing mechanical or electrical has failed but only way to fix is disconnect battery for a second. Or replace parts and hope for success
One thing we have experienced that is totally off the rails on any account is Our error occurs almost exclusively in the same precise geo location every time. 34.13552° N, 84.76025° W
No conspiracy theory but there is something weird happening in this area if 19 out of 20 times passing thru we’ve had to do the battery trick because of error that occurs like clockwork at this particular location.
Something about this location must be interacting with ECM or interrupting a clean signal from sensor. All I can imagine is some geological electro-mechanical dead zone or if you’re conspiracy minded something far more nefarious.
If someone else has experienced a similar situation at a particular location, I would love to try and understand this mysterious occurrence.
We love our Acadia - We just need an exorcism