To everyone in this forum: After a year of headache, I finally figured out what the issue is. Yes, it is the thermostat, but you have to get it replaced from the dealership with the newer thermostat that GMC came out with after many complaints. The old replacement part that you get from AutoZone or even the first dealer I went, is the problem in the first place. There is a new updated thermostat GMC came out with to directly solve the issue for good.

Also, with all the wear and tear that it does on your vehicle while the bad thermostat is going bad. It drains your battery, completely kills your battery. In that case once you do get the right new thermostat your car will begin to go haywire and start throwing all these codes, not wanna start, and you kind of feel like you’re back at square one. No, you actually know at that point that you have solve the problem and what it’s doing is it shutting down everything in your car and going into battery saver mode because your battery is damaged and can’t withstand all the features that your truck has.

You’ll go to AutoZone to check your battery they’ll tell you your batteries good yes your battery is good but it’s not good enough for your vehicle with all the bells and whistle‘s and steering assist, touchscreen, power seats and every feature this truck has. You have to go get a new battery after getting the corrected new thermostat from GMC.

P.S. THIS IS COVERED UNDER YOUR POWERTRAIN WARRANTY AND THE THERMOSTAT WAS FIXED COMPLETELY FOR FREE AT THE SECOND DEALERSHIP I WENT. THE FIRST DEALERSHIP ****ED ME AND CHARGED ME WHICH IM IN THE PROCESS OF GETTING MY MONEY BACK FROM GMC FOR THAT OUT OF POCKET COST THAT WAS COVERED UNDER THEIR WARRANTY. Hope this helps everyone out there!

 

To everyone in this forum: After a year of headache, I finally figured out what the issue is. Yes, it is the thermostat, but you have to get it replaced from the dealership with the newer thermostat that GMC came out with after many complaints. The old replacement part that you get from AutoZone or even the first dealer I went, is the problem in the first place. There is a new updated thermostat GMC came out with to directly solve the issue for good.

Also, with all the wear and tear that it does on your vehicle while the bad thermostat is going bad. It drains your battery, completely kills your battery. In that case once you do get the right new thermostat your car will begin to go haywire and start throwing all these codes, not wanna start, and you kind of feel like you’re back at square one. No, you actually know at that point that you have solve the problem and what it’s doing is it shutting down everything in your car and going into battery saver mode because your battery is damaged and can’t withstand all the features that your truck has.

You’ll go to AutoZone to check your battery they’ll tell you your batteries good yes your battery is good but it’s not good enough for your vehicle with all the bells and whistle‘s and steering assist, touchscreen, power seats and every feature this truck has. You have to go get a new battery after getting the corrected new thermostat from GMC.

P.S. THIS IS COVERED UNDER YOUR POWERTRAIN WARRANTY AND THE THERMOSTAT WAS FIXED COMPLETELY FOR FREE AT THE SECOND DEALERSHIP I WENT. THE FIRST DEALERSHIP ****ED ME AND CHARGED ME WHICH IM IN THE PROCESS OF GETTING MY MONEY BACK FROM GMC FOR THAT OUT OF POCKET COST THAT WAS COVERED UNDER THEIR WARRANTY. Hope this helps everyone out there!

Was having same issue with my 2019 Acadia Denali- Have had battery issue for the last few years. Thermostat has been intermittent. Acting up again lately and was going to pay a local garage $1200 to fix. Saw your post and read that it is covered under power train warranty and called the dealer and they are going to cover it!! Thanks for your post! You saved me $1200!

 

Also I went ahead and bought a top of the line Optima Battery with 800ccc. Cost me about $350, but it’s got my truck driving like a dream come true, has more power than ever, and was worth every copper penny.

 

How is it your thermostat when it does it at first start up? Engine hasn't even started to get warm yet. Very first thing that comes up. A thermostat doesn't even start to work until the engine gets upto 180 degrees or whatever its set at. Its an electrical issue im convinced. Battery terminals or computer. But taking off the terminals always resolves the issue.
If your battery is getting corroded than it might be leaking gases internally.

 

How is it your thermostat when it does it at first start up? Engine hasn't even started to get warm yet. Very first thing that comes up. A thermostat doesn't even start to work until the engine gets upto 180 degrees or whatever its set at. Its an electrical issue im convinced. Battery terminals or computer. But taking off the terminals always resolves the issue.
If your battery is getting corroded than it might be leaking gases internally.

I think you read my post wrong, re-read to answer your own question.

 

My battery is new and i haven't had any problems with it either. No other codes.. Hope everything is good for you.

 

new to forum but not to the car game. I have been dealing with this same issue for a little over 1 year.. after reading thru the thread I realize no-one is finding the common instigator of the issue. I have determined what causes the message to pop up, fans to run, a/c to stop running and general chaos that happens when your wife is driving along and things go to crap.

Ours is a 2017 SLT and the only time it comes on is when the outside temp is under 65 Degrees F. then the fun begins.. I have had it start anywhere from 2 to 20 miles into a cool temperature drive. it is easy to make the situation end buy disconnecting the battery for 30+ seconds. it will make it all stop until you have a cold weather drive (i know in many places of the world 65 F is NOT cold.. but it is here in Cali lol).. once you have this temp event the whole thing starts over again... I am finally breaking down and going to the stealership tomorrow, i know they are going to try and make me bend like a pretzel and take my credit card for all it is worth but, I am tired of my wife hiding my 10MM wrenches because she can't find one (10mm the hardest size to keep in your toolbox).

Things I am taking away from this thread are as follows, a potentially redesigned thermostat, sensors are a pain in the azz to locate (yes I have tried as well and gave up), and no-one is 100% on a specific repair for the problem but the symptoms have been getting handled (all the things that happen when the message comes up).

If anyone can look into their personal history with this issue and confirm that it only STARTS when it is colder then 65 please let me know...once the error starts it doesn't normally go away although I have seen a couple rare instances when it went back to normal by itself.. normally it requires a system reset (battery disconnect) to clear the issue. well here we go... to the stealership and hoping it's not going to hurt...maybe i'll bring some lube just in case they don't offer any..

As a side note, in my setting up the appointment i started grilling the service guy about possible issues and he instantly homed in on the thermostat housing. I am aware of a potential TSB addressing the calibration of the temp system and i'm hoping for to just need a calibration flash.

 

I actually had my thermostat replaced abouta month ago, under the factory warranty.. It's been fairly cold the past couple weeks here, and no error had come up yet.

 

got home from stealership... glad i brought the lube because this is painful.. apparently you have to remove the intake manifold to access the thermostat!!! this repair is going to involve replacement of the thermostat, housing (thermostat is built into the housing and requires the replacement of both), sensor, and the fluid. i found a video that shows the thermostat service being done (

)... i had to look it up because i felt like the stealership was pulling the most insane con job on me when he told me the manifold had to come off. in the video he says GM made a change on the newer models and moved the thermostat to the driver's side of the engine by the radiator hose, but alas i have an early build 2017 model so mine is buried under the manifold... for the price i am paying for this service it had better fix the problem!!

so lets check something else out, anyone who is having this issue what is the build date on your car? i'll grab my build date off the label when i get her back from the dealer.

 

Thanks for the feedback. Wow. . what an ordeal just to change the thermostat.

 

yeah it's crazy. the service has been completed but i need to test the car with the outside temp conditions in the range i know it triggers the problem with to make sure it actually fixed the issue.

 

If you don't trust the dealer, like the pricing, or want to tackle it yourself, why not go to an independent mechanic? There shouldn't be any programming needed for this work.

 

i was told there could be a calibration issue so it could have been a programming issue..in general i don't trust shops but once it was completely revealed that the manifold had to be removed i was not going to take the risk of breaking the plastic manifold and do it myself. The car has 105k miles on it so plenty of heat cycles that could potentially make the plastic brittle.

 

The latest update. My 2017 acadia started getting the power assist message and temperature gauge drop everyday. So when i get home i would keep taking off the negative battery terminal and retighten it. Clear the fault and drive again. I finally realized that i was tightening it down to tight and put a groove in the battery terminal. So as i was driving the negative terminal would loosen just a bit and the message would pop up. The last time after a week of dealing everyday with it i installed the negative terminal in a different spot off of the groove and torqued it down to correct value. Now for the last month or so i haven't had any more issues. Makes me think it was the terminal the whole time after dealing with it everyday. It was always tight enough to start and run the other systems but still loose enough to throw up the message and shut down the air conditioning.

 

what have your daily outside temps been like?

 

update on my situation. i finally got the opportunity to drive the car in sub 65 degree weather yesterday after having the service performed.. well, it did not trigger the assist alert or any other of the issues that come with it. For now i am gonna consider my situation to be working.. i want to see it cycle in cool temps a few more times without issue before i say fixed 100%.. i am 90% sure it would have faulted out if i had driven it yesterday without the service done.

 

My wife has the 2017 Acadia Denali and this issue happened to me today. This morning the Steering Assist was displaying then on the way home I noticed that AC wasn't cooling then noticed the temp gauge was down. Hoping this will be a easy and quick fix?

 

Take the negative battery terminal off and re install it. Should clear it. Make sure its not dirty.

 

I noticed that sometimes there are problems with the air conditioners. Especially on cars.An old air conditioner? System outages? Or is it already a malfunction due to long years of operation? My friends from this company airconservicing.org they gave me the answer to this question. Although they are experts in air conditioners located at home, they can also help with the car. In general, the problems may be in system outages. But, fortunately, it is quickly repaired without any problems. However, there may be a problem with the system update.

 

I noticed that sometimes there are problems with the air conditioners. Especially on cars.An old air conditioner?

There are many reasons for this. Read this whole thread and search for others like it here on the forum.
Leaks in A?C system o-ring fittings and elsewhere often develop as a vehicle ages.

 

I guess I'll join the party!
2018 Acadia SLT 45k miles
Driving to work this morning about 75 degree weather in North Florida 5:30am since I'm giving all the specifics.
7 miles from the house, jumped on the highway and immediately get Steering Assist Reduced. Then I immediately noticed the temp gauge at 0. Then the AC went out. Fans on High
Found multiple forums and looks like multiple people have multiple answers.
At this point I just drove the other 7 miles to work. In the meantime, I found the answer about taking the negative cable off. This did indeed reset everything back to normal, just haven't drove anywhere yet.
So now the question, do I dive in and replace the Temp Sensor, replace the thermostat as well, or go with the thinking that the UNCORRODED battery terminal is the issue?
What has someone's firm resolution been to never having the issue arise again?

Between the Reverse light LEDs destroying my battery , the transmission flares from 2nd to 3rd no one ever figured out, the shift to park issue which I know is a hour long but simple fix, and now this, I'm regretting buying this Acadia 6 months ago.

Also, what sensor is in the attached photo? Not the temp sensor right or? Because that looks to easy to replace if it is indeed the location.

 

...
Also, what sensor is in the attached photo?

Looks like an oil pressure sensor.

Read reply #3 in the thread linked to the post just above yours. The owner describes one seemingly viable solution to the "Steering Assist Reduced" (plus) problem. It appears the solution is covered by GM's new car power train warranty, so you don't have to DIY anything if your vehicle meets the warranty criteria.

 

My 2017 Acadia Denali was having intermittent Power Steering Reduced and no AC. The dealer tried to get a code but it didn't save. Yesterday it came back on so I drove it straight to the dealership. It is a mile away and n to the time I arrived, there was no AC, and fan was running high. it looked like it was overheating. They gave me a loaner and are in the process of replacing it the thermostat. Supposedly to get to the thermostat they are having to remove the injectors. I am not sure what all they are replacing but stated some parts won't be in until Monday.

 

Is this problem better to fix in a dealership?

Any skilled technician should be able to do the job. Best to go through a dealership if the vehicle is still under warrnty, though.

 

Glad to see you avoided a costly and unnecessary expense by checking the battery and its cables.

 

Glad to see you've had success. I did also replace my battery which was towards the end of its warranty. Be aware of your battery's age also.

 

I'm glad I found this thread. I recently experienced the same issue (reduced steering, cold engine, fans running, engine light, P0128 trouble code). The issue started in cold weather (around 45 degrees) while driving on the freeway. I have a 2017 Acadia Denali with about 75k miles. I was about to take it to the dealer to get the thermostat replaced, but I tried cleaning the battery terminals and disconnecting the negative. I did this about a week ago and have had no issues since that time. My battery is 2 years old. If the issue comes back and persists then I may get the thermostat replaced, but I'd prefer to avoid the cost of that repair.

 

Good to have yet another find this seemed to resolve this issue.

Please do return and keep the forum posted if the problem has stayed away.

 

You should definitely have your battery tested; if it's weak it may need a replacement. That was my issue as my problem has not returned. This solution may save you a few bucks. Additionally, you may want to replace the battery cables; a cleaning may not be good enough. Good luck!

 

Have a dealership appointment monday for ECM reflash.

Keep it simple first people.

Batt. Connections (Cheap), Batt up to snuff ($150), reflash ECM for latest revision ($125) , revisions aren't made just because engineers enjoy programming.

About the redesigned thermostat. If it is sticking why are you never seeing overheating & Just lost temp feedback. It could cause an air pocket, but you would see temp fluctuations before that. (the sensor is not in the thermostat housing) The vehicle shouldn't maintain temp with fans alone if it is partially stuck, also if it's partial you'll have some coolant flow which would should prevent the air pocket. I've seen weirder stuff though.

In my 20+yrs. experiance in industrial controls/electrical, our main culprit of off the wall crazy **** nowadays is firmware & needing to upflash to solve issues that arise, even years after install. Why? Nothing is as good out of the box like it used to be. Let's just see how complicated we can make things & how many computers can we add & then tie them all together with some complicated comms protocol & a single, nonredundant, tiny coaxial cable. And to top it off, lets make sure most of our design engineers started straight out of school with no real world hands on experiance.

Well that's my RANT, Sorry. If anyone truely resolves this issue please post so that some of us can regain our sanity.

Thank You to everyone who has posted, this thread has benn very helpfull.

 

We have a 2017 Acadia Denali and last week before leaving on vacation I started to notice just the "steering assist reduced" message. Then after we got back from vacation, we started to drive home and the temp Gauge bottomed out and A/C didn't work along with a check engine light being on.

I had scheduled a appointment with a local shop but then found this thread. Went home last night and gave the removing of the Neg terminal and cleaning it thing a try. Drove it to the car wash last night with no issues and the AC was blowing ice cold air. Then drove it all the way into work this morning and everything seemed fine. Sure hope this sticks as I don't want to drop over a grand on this car again. For now I canceled my shop appointment.

I've had nothing but gremlins with this 2017 Acadia Denali. "Shift to Park" message, Getting locked out even with the keyfob present, Leaky AC system, Leak in my rear center tail light, strange software behavior all the time. The list goes on and on. Now this stupid thing.

 

Just had ECM reflashed to latest rev. per tech note & it's back. Wouldn't read temp & fans on after multiple restart's. Disconnected battery & it cleared. Tells me there is programming that could have been changed in the latest rev. since I know **** well GM knows of the issue. They could have the ECM just rescan for a temp reading after a couple minutes instead of latching in the fault state since they can't just figure out the **** problem instead of giving out B.S. fixes that cost money & don't cure the issue.

Cross off: Temp Sensor, Thermostat, temp sensor wiring, batt. conn.

Possible bare wire or pin shorting on something to ECM that has nothing to do with the 2 temp. sensor conductors is where I'm at now. Still want to blame the ECM. It's been flashed to latest rev., so even if that is the culprit there is no fix or use going down that road. May try another temp sensor just for the hell of it, but it's slim.

I will also have the battery tested even though it's new. Could be something draining the voltage just low enough intermittently to screw with the ECM & it's just a coincidence it screw's up the temp scan when it happens. (also motor grounds, even though the sensor has no reference to ground)

For the shift to park, there are a couple youtube vids. One is how to get the shifter knob off so you can re-insert the pin that walks out & super glue it back in place. ( Which I've had to do). The other shows the wiring harness & how to bypass the Park switch, which I am doing as soon as I get time. The super glue held for a year. The switch bypass doesn't seem to affect anything.

All in all, it's a very nice vehicle & we plane on upgrading to a 2022 Denali soon.

 

I have noted on this post and other posts that changing the sensor did NOT fix the issue. Anyone find another cause? Fixed? Thanks.

 

Does anyone know which relays might control the temp sensor/cooling systems? We’ve been having this problem for quite some time. We just so happened to replace our battery a couple of weeks ago and this problem still came back. Our fix right now is to pull the negative cable for a few mins and then reconnect and the car runs fine for 1 week. The problem comes back every week without fail. Its quickly becoming one of my “sunday chores”. Its got to be an electrical / software issue of some sort.
We also have the shift to park deal but haven’t bothered to spend the time fixing it. Did see the you tube fixes and will address it later. Or maybe we’ll trade it in on a new a Yukon XL. Dealership can deal with it at that point.

 

I've noticed on my 2017 acadia it was doing this every week also. Sometimes every couple days. I've noticed that the negative battery terminal only tightens around the base of the battery terminal. And it always is loose again when i remove it. So the last time i did it i took some pliers and squeezed around the top of the terminal so it will fit tighter on the battery stud. I than re installed the negative terminal. It seems to have helped it because my weekly chore has stopped. Well wait and see