Did you ever resolve this issue? Im having the same problem.

 

No, we were driving to the dealer and the problem went away, so they couldn't diagnose. It just came back this week. I may try a thermostat replacement this weekend if I can find it. Did you have any luck?

 

I did. I replaced my thermostat about a month ago and my problems went away. This seems to have fixed it. Replacing the thermostat was a difficult task and took me about 4 hours, but you can do it. You need to remove the items off the top of the engine, like the air intake and even the fuel rail, then the thermostat is under that. The thermostat is about a $150 part because you get the housing and pipe with it.

 

Thanks for the info. Did you flush air out of the radiator/coolant system after? If so, how?

 

I did not need to. I just refilled the overflow bottle a little past the full line and started the engine and let it idle for a while. It circulated the coolant and I had to add a little more in, but not much. Just keep an eye on the level over the next few times of driving it and if the level stays full, you should be fine.

 

My Acadia just started this...They quoted me 2000 to fix the issue, I can handle time and frustration or even to buy the part and find a travel mechanic because 2000 at christmas.....whew

 

This week I had the same problem with the steering assist code, engine light and the car was roaring at startup.They replaced the thermostat and it works fine. They said the steering assist goes through some of the same modules so that is why it showed up but nothing was wrong with the steering.

 

Has been happening off and on also. I take it to dealer they do something to the software, since they can’t find any codes wrong with it. Problem comes back in 3-4 months. This has happened twice before, BUT now I’m getting ’service the engine’ light also 😏

 

I’m having the same problem with my 2017 acadia. It’s no longer under warranty and they are quoting me $900 to fix.

 

$900 to replace the Thermosta?

 

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.

 

I had the same issue after working under the hood, changing the oil and filters. I simply reseated the connector to the ETC sensor and the code went away. I wiped off the terminals and blew them out with an air compressor. Maybe it came lose or collected too much dust. Definitely check your connection before spending lots on parts and labor. The sensor itself is less than $10 and pretty easy to get to. I haven't touched my thermostat yet.

 

Where did you find the ect?

 

I am having the same issue on my 2017.

 

My update, I had a great mechanic change my sensor, with 1.5 hours of labour. The dealership has it as 4.5 hours. It wasn't the problem, so now I will get him to change the thermostat. The dealer told me that the thermostat regulates the flow to the sensor, making the sensor seem to malfunction. Might be worth changing both at once for everyone else who has this issue.

 

I have a 2019 Acadia SLT-1 V6. I keep getting the steering assist code and my fans run high and my AC blows hot. I had my car at a dealership (one that I dont normally use) for another reason that I am not paying for and they informed me while they were already diagnosing my car for another issue caused by a accident. They told me that I need to replace my thermostat and quoted me $725. I called the dealership I normally use and they quoted me to replace thermostat $515 and change out the door. I know the part before tax is $146.47 from GMC dealer. I just want to make sure that this is going to fix the problem. I live in Florida and its hot and I need my AC and love my car and want to make sure this will fix this the first time and not spend all this money if I don't need too. What do ya'll think that I should do? I am taking it in Thursday to my regular dealership to have them diagnose it and they said they won't charge me that $155 fee if I go ahead with the thermostat replacement.

 

I have the same issue with my 2017 Acadia. It only does it on the the interstate and not local driving. My gmc dealership quoted me $900 and then a local garage quoted me half. I was told it’s mainly labor fee because of where the thermostat is located. Apparently, these cars are known to have that issue. Good luck!

 

could you let me know where can I get the acadia t-stat?

 

My 2017 is doing the same thing. It just seems fishy as it started right after my warranty expired. GM knows what is going on as I see it happening all the time. Bad part is you can no longer find the thermostat online and my dealership quoted $1500 to fix. This will be the last GM product I ever own.

 

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.

 

Yep, worked for me. Well you cannot tell me it is a thermostat issue (as the dealership has). I am not too proud to just keep removing the negative cable every time it happens. Sure does beat spending $1500 on a problem that will not be fixed anyway. Love this forum and huge thanks to Mike.

 

Ok guys removing the negative cable resets the issue but it keeps coming back. Is there anything else that needs to be completed? Update, etc...

 

Follow what the dealer's service center has told you. Seems to have worked out for a lot of folks. Read through the other threads about it and you'll see. You just might enjoy some humble pie. lol

 

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

 

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.

 

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.

 

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 .

 

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.

 

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 😂

 

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.

 

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?

 

Enough is enough. After fighting the P0128 demon for a year, I'm diving into the repair this weekend. I actually found that when I would hook my code reader up, if I erased the P0128 code the thermostat and AC would instantly come back and the "Active steering" warning would stop, but then it would act up again 2 - 3 weeks later.

I'm at 88.5k miles and spark plugs are due at 90k, so as long as I have to take the intake off, I'm going to do the spark plugs, thermostat, temperature sensor, intake gaskets, engine filter, and cabin filter all at once. OEM parts for everything ran $258 on Amazon (I was skeptical, but everything looks OEM and came in GM packaging). Dealer wanted $1400 for the thermostat and $407 for the plugs, so I figure I'm trading one weekend afternoon for $1,500.

As long as I've got the top half of the engine apart, is there anything else I should consider replacing? I've already watched all the youtube videos on this-- any last minute suggestions? Thanks, all!

 

Make sure you also have new o-ring seals for the "water outlet" thing that attaches ( and needs removal) near the T-stat.

Complete parts needed listed earlier in this thread:

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

 

Welp, I did it all and everything went back together really well... or so I thought. The error is gone, and I'm very glad I did the spark plugs while the intake was off, that was easy. It's running fine, but unfortunately now I have a small coolant leak. I suspect it's coming from the temperature sensor that I didn't get tight enough. That temperature sensor is in a horrible spot, but with the manifold off I could get a 15 mm wrench on it. I was afraid of over tightening, but I've seen a few drops of coolant around the sensor after driving, so I'm afraid I didn't get it tight enough. (I've also considered that I over tightened it, but I think that's less likely.) After driving for 30 minutes I'm seeing 2 or 3 quarter-sized puddles under the car, and after a day driving, the coolant reservoir is about 1/8" below full. Definitely not sustainable.

Any one have a torque spec for the temperature sensor? The only recommendation I saw was 10-15 ft./lbs, which lacks the specificity to convey any confidence.

My plan is to 1) Buy the 15 mm Duralast socket 1/4" drive and a 1/4" universal joint to tighten the sensor a little more, hopefully without taking the intake manifold off again. Drive for a few more days and see if that corrects the issue. In the mean time I've been adding a couple ounces of coolant every night. 2) If that does not work, I plan to take the intake off again and replace the temp sensor, on the off chance that I over tightened it and the crush washer is bad.

Nightmare isn't over quite yet.

 

Welp, I did it all and everything went back together really well... or so I thought. The error is gone, and I'm very glad I did the spark plugs while the intake was off, that was easy. It's running fine, but unfortunately now I have a small coolant leak. I suspect it's coming from the temperature sensor that I didn't get tight enough. That temperature sensor is in a horrible spot, but with the manifold off I could get a 15 mm wrench on it. I was afraid of over tightening, but I've seen a few drops of coolant around the sensor after driving, so I'm afraid I didn't get it tight enough. (I've also considered that I over tightened it, but I think that's less likely.) After driving for 30 minutes I'm seeing 2 or 3 quarter-sized puddles under the car, and after a day driving, the coolant reservoir is about 1/8" below full. Definitely not sustainable.

Any one have a torque spec for the temperature sensor? The only recommendation I saw was 10-15 ft./lbs, which lacks the specificity to convey any confidence.

My plan is to 1) Buy the 15 mm Duralast socket 1/4" drive and a 1/4" universal joint to tighten the sensor a little more, hopefully without taking the intake manifold off again. Drive for a few more days and see if that corrects the issue. In the mean time I've been adding a couple ounces of coolant every night. 2) If that does not work, I plan to take the intake off again and replace the temp sensor, on the off chance that I over tightened it and the crush washer is bad.

Nightmare isn't over quite yet.

I agree. . maybe use the universal and tighten a bit more.
Did you use any sealant on the temp sensor threads?

Although, if I recall looking at it. . . appears it is a tapered pipe thread so tightening a bit more may do it.
Also, it could be leaking from one of the o-rings?

 

.

 

Update - Yesterday, about 12 minutes into the morning errand drive, got the steering message, water temp dropped to cold, etc. I've been driving with the scanner hooked up for the past month observing the coolant temp regulating between a normal low of 165-167 driving around our little town at speeds of 35 - 55 mph and normal high on hot days with the AC running 180-187. When the "event" happened this morning the scanner coolant temp was at 165 and there was only one code, the P0128. I have previously replaced the temp sensor and the harness. New battery as well. From my observations over the past month, the thermostat is not sticking. Driving with the scanner hooked up, I have watched it regulating. I cleared the code with the scanner and it's operating normally.
We've had our Acadia since new and this problem first showed up at about 75K. We are now at 83k and It has been intermittent, sometimes going months / hundreds of miles between events.

• So, has anyone fixed this with just a thermostat / sensor / harness change?
• Has anyone fixed this with just an ECM update?

Is it po$$ible that, when a dealer is doing this, in or out of warranty, they are replacing these parts AND also complying with Bulletin No.: 17-NA-390 ECM update?
Thoughts?

 

I'm thinking since we both have a 2019 they would not do the 2018 ECM update.

But that may still be similar or the same issue with a 2019 ECM ?

I guess, try and take it to a dealer who is agreeable to look at your findings and see if they would contact GM tech support for this issue?

Also, the 75K miles or there abouts seems to possibly be relevant?
Or. . .. is it AWD and FWD models affected or relevant?

I have not had this appear yet.