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So, it looks like you guys have nailed it on the 2014 Acadias ---- Engine Coolant Sensor needs replacing. I am helping a neighbor with a 2017 that appears to have the same issues ---- dash temp gauge reading cold, radiator fan running continuously from start-up and air conditioning running warm. Also have a warning on the dash saying "Steering Assist is Reduced" and a P0128 check engine code that says "Coolant Thermostat (Coolant Temp Below Thermostat Regulating Temp). I suspect this is still part of the same issue, because they all showed up at the same time. GMC must've made a major engine change around 2016-17 because the engine compartment looks completely different than what I'm seeing on your enclosed videos. And I can't seem to find any videos or chats on the 2017s. So, my main question is "Where is the engine coolant sensor located on these newer engines?" I hope no one else is having this problem on their 2017 through 2019, but I hope someone knows where to start looking for this sensor. I don't really care to go ripping off all kinds of engine covers just to find it.
Thanks,
Gene
You can find Haynes repair/maintance. Books for GMCAcadia up to 2017. But they don’t make any books for the Acadia after 2017. Arcadia is a 2018. My husband was raised in a garage with his father and can maintain our cars quite well. However these newer vehicles I’ve got them stumbling. This sensor he cannot even locate because we can’t find a manual to tell us where it’s at. And all the videos we find on YouTube are for older models so it’s no place we’re near where they’re saying it should be. Can anybody tell us where the sensor is on a 2018 Acadia?
I know he can replace it if we can find it.
we went and purchased a download for the 28 Arcadia which was some 600 pages. However there’s no directories on telling you which page you’re gonna find your issue want. Biggest waste of $30 we ever spent because neither him nor I have time to sit there and scroll through page after page after page on our computer to try to find the issue.
Don’t know what kind of deal Haynes made with GMC do not produce a book for them anymore but it must’ve been really worth it because they’re screwing all their loyal customers.
 

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Also 2018 GMC Acadia. Same problems. Haven't checked engine code but light does go in and out intermittently but seems to stay on longer than out. I have found by shutting engine off and waiting until until the fans stop running and then restarting the vehicle with reset it to get the thermostat gauge and ac running again but the problem keeps coming back. I'm going to pull the negative battery cable tonight since this is one of the reads. But thinking why GM would of came out with a upgraded thermostat if the old ones were not a problem.
 

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Dont waste your time with the sensor. Bite the bullet and replace the thermostat. That will fix the problem. It doesn't seem right, but I replaced my sensor first and still had the problems. I then replaced the thermostat and I've been driving the vehicle for 2 months and have not had any issues. I wasn't to optimistic about replacing a mechanical item to fix these issues, but it worked.
Thanks for posting your updates. We've been having the same issues, just replaced the sensor and of course the next day we were back to the same problem. I guess next step will be replacing the thermostat. What a pain and GMC has been no help besides taking our money.
 

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I am having the same P0128 issue on my 2017 All Terrain and trying to decide next step. The battery terminal removal and cleaning worked for about a week and got me home from 10 day vacation (several hundred miles) but the "power assist" notification and high speed fan came back yesterday. After reading all 7 pages of comments here and many other related posts on the potential fixes I am not sure changing sensor and/or thermostat will fix the problem. It would be great if more people would PLEASE POST WHAT DID WORK LONG TERM. I really don't mind doing almost anything if/when I know it will work but these "sometime" fixes/issues are the worst. I love my Acadia but after dealing with the 1-2 trans flare for five years with no fix, this may be the deal breaker. Any conclusive feedback on your successful fix to this P0128 issue would be appreciated. THANKS!
 

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2017 Acadia Denali, I love this truck BUT, I wonder if I bought a nightmare. I have the shift to park assist alert, which I learned just needs a flick on the shifter knob while pushing forward to clear. Seems shifter knob or micro switch or both changed fixes this issue. AND today I got a repeat message, steering assist is reduced alert, AND I noticed my AC was not working at the same time. I came in and read this entire thread, went out and found my negative battery terminal corroded, I cleaned it off, which meant I had the terminal off for over a count of 10, and put it back on. I learned that this resets the PCM. Steering assist is reduced alert is GONE and AC is WORKING. The battery looks new, but I am going to have it load tested. Also, even after I tightened the 10mm nut to the point that I thought it was going to brake, the terminal still seems to not be tight enough on the post. I will be having that checked too. Does that slide mechanism that tightens the battery terminal to the post need lube? I just bought this Denali, and I love it. I want it to be dependable. Someone please tell me that these problems once fixed make you proud of your purchase!
 

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How do I put 2019 Acadia Denali under my Miltp920?
How many mileson your Acadia?
Too enter your vehicle info, go to your account settings and enter the info in the signature. That should post it in two places.

Did you buy your Acadia Denali new ? Did anyone change the battery in the past.?

Those type of battery connector should not be over tightened. They will stretch the metal and then never work correctly again.
So if someone installed another battery sometime in the past and over tightened it. . . it will need replacing of that connector.
 

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How many mileson your Acadia?
Too enter your vehicle info, go to your account settings and enter the info in the signature. That should post it in two places.

Did you buy your Acadia Denali new ? Did anyone change the battery in the past.?

Those type of battery connector should not be over tightened. They will stretch the metal and then never work correctly again.
So if someone installed another battery sometime in the past and over tightened it. . . it will need replacing of that connector.
I have 76000 miles and I just bought it. I am the 4th owner. The battery appears new, but I could not see a date on it. I will take it to my mechanic and ask about tightening, or replacing that negative terminal. It looks like electrical issues are a common Acadia issue, reading this forum. I wish I would have read this thread better before I bought the car. It is so beautiful and clean with all the options I wanted. I had a reliable 2016 Denali 3500, I just assumed it was a solid car. Maybe it is, and I just need to fix the battery connections.
Are you having any issues with your 2019? I put 2019 in my username after reading your username, but mine is a 2017. I am trying to get my user name changed again to include 2017..LOL
 

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I have 76000 miles and I just bought it. I am the 4th owner. The battery appears new, but I could not see a date on it. I will take it to my mechanic and ask about tightening, or replacing that negative terminal. It looks like electrical issues are a common Acadia issue, reading this forum. I wish I would have read this thread better before I bought the car. It is so beautiful and clean with all the options I wanted. I had a reliable 2016 Denali 3500, I just assumed it was a solid car. Maybe it is, and I just need to fix the battery connections.
Are you having any issues with your 2019? I put 2019 in my username after reading your username, but mine is a 2017. I am trying to get my user name changed again to include 2017..LOL
A loose or faulty battery can cause many issues.
Generally from reading through the forum, and the gauges act wonky plus no heat or A/C . . . it seems a battery issue or the engine thermostat and coolant sensor next to it may need replacing.

Did you buy it from a GM dealer? If you only had it 4 months take it back there? No warranty?
 

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2018 Gmc Acadia SLT here. 80k miles. Having this exact same problem for about a month now. The car does seem to do this when there’s a big outside temp change. Saw many of the replies on here saying to disconnect battery terminals and it should fix the issue. Just tried it. Had a small amount of corrosion on terminals. Cleaned it off and reconnected. Vehicle is working fine now and steering assist reduced message is gone. Engine temp getting a reading of normal range. Will see if this comes up again in the future. Looks good for now.
 

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2018 Gmc Acadia SLT here. 80k miles. Having this exact same problem for about a month now. The car does seem to do this when there’s a big outside temp change. Saw many of the replies on here saying to disconnect battery terminals and it should fix the issue. Just tried it. Had a small amount of corrosion on terminals. Cleaned it off and reconnected. Vehicle is working fine now and steering assist reduced message is gone. Engine temp getting a reading of normal range. Will see if this comes up again in the future. Looks good for now.
I am in the same spot, with 76000 miles on a denali. It has been a few days, and not return of steering assist alert. I expect it will come back and eventually we will have to replace the thermostat and temperature sending unit. I read somewhere, probably in this thread that the temperature sending unit or thermostat sends a signal to the ECM and it is low temp (false) and the AC shuts down to preserve power, the steering assist comes on because in COLD weather the fluid gets more dense and it is harder to steer your car. But it is all false, becuase the temp/thermmostat is sending a bad signal I guess GM redesigned these parts and we have to buy GM parts to get it fixed, or chance it repeating. So, until we decide to get it fixed, I carry a 10 mm wrench with me to disconnect the negative terminal to reset if for an unknown at this point, amount of time. I also think I read that it might be covered under the power train warranty, so I will be looking into that too, because I think it is a $900 dealer repair, labor intensive.
 

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A loose or faulty battery can cause many issues.
Generally from reading through the forum, and the gauges act wonky plus no heat or A/C . . . it seems a battery issue or the engine thermostat and coolant sensor next to it may need replacing.

Did you buy it from a GM dealer? If you only had it 4 months take it back there? No warranty?
A loose or faulty battery can cause many issues.
Generally from reading through the forum, and the gauges act wonky plus no heat or A/C . . . it seems a battery issue or the engine thermostat and coolant sensor next to it may need replacing.

Did you buy it from a GM dealer? If you only had it 4 months take it back there? No warranty?
I bought it from a car sales lot that got it from auction. I am looking into a 12 month warranty they said I have , I think on power train. Otherwise, used car, sold as is. My luck. Beautiful Car, its a shame.
 

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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!
 

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Ten days after replacing thermostat and coolant temperature sensor on my 2017 Acadia all the various issues such as power assist warning, a/c hot, cooling fan high, temp gage on C are now gone! I will post again in near future if this fix is truly LONG TERM since my first fix, disconnecting and cleaning battery terminals, lasted for only about 5-6 days. I used a Doorman thermostat assembly from Amazon since it was quite a bit cheaper and I discovered during repair that Doorman thermostat housing (right) had a GM part number cast into it very similar to my original (left).

Also, if your car is near 100K miles I would suggest changing the spark plugs at the same time since the intake manifold must be removed to replace the front three plugs.

Household hardware Auto part Metal Gas Fashion accessory
 

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Ten days after replacing thermostat and coolant temperature sensor on my 2017 Acadia all the various issues such as power assist warning, a/c hot, cooling fan high, temp gage on C are now gone! I will post again in near future if this fix is truly LONG TERM since my first fix, disconnecting and cleaning battery terminals, lasted for only about 5-6 days. I used a Doorman thermostat assembly from Amazon since it was quite a bit cheaper and I discovered during repair that Doorman thermostat housing (right) had a GM part number cast into it very similar to my original (left).

Also, if your car is near 100K miles I would suggest changing the spark plugs at the same time since the intake manifold must be removed to replace the front three plugs.

View attachment 12401
Thanks for this post and information. I am in the same boat you are but have not made this repair yet. I am following to see if it is a LONG TERM fix also. I am about 2-3 weeks since I did the negative battery cable and no return steering assist message, yet. I figure I am going to have to make this repair also, 2017 Acadia Denali. My mechanic said it is a remove intake job, Now I know to do spark plugs too, I am at 76K miles. Do you part number for Amazon, I did not know amazon sold car parts, lol!
 

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Thanks for this post and information. I am in the same boat you are but have not made this repair yet. I am following to see if it is a LONG TERM fix also. I am about 2-3 weeks since I did the negative battery cable and no return steering assist message, yet. I figure I am going to have to make this repair also, 2017 Acadia Denali. My mechanic said it is a remove intake job, Now I know to do spark plugs too, I am at 76K miles. Do you part number for Amazon, I did not know amazon sold car parts, lol!
Here you go - - Complete parts needed.
Problem . . .No A/C, Power Steering Assist Reduced/Disabled notification, Fan running all the time, Engine Temp at 0, and P0128 Code.
Go to the dealer or online parts site 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 ( Or GM Genuine Parts 15-11122 )
Engine Temperature Sensor (might as well replace this $12 part at the same time) *This one you can get anywhere Part# TX281
 
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