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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!
We're having this issue with our 2017 SLE. We had the thermostat sensor replaced, but that didn't help. My question is: Does it hurt the engine to drive the car when these symptons happen? Temp guage drops to zero, fan blows high, steering asst. etc.
 

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On some cars when the thermostat faiks open, the engine runs rich, as if it were a cold engine.
Monitor to see if you can tell if engine idle is higher than normal.
The computer may have a default operation when this is detected.
 

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We're having this issue with our 2017 SLE. We had the thermostat sensor replaced, but that didn't help. My question is: Does it hurt the engine to drive the car when these symptons happen? Temp guage drops to zero, fan blows high, steering asst. etc.
You can read a quite a bit about all of this searching in this thread. It sounds like too common of an issue. I will tell you what I think, because the sensor thinks it is too cold, it thinks that the grease in the steering box is more dense and your electric steering capability will be "reduced". So, your steering wheel might be a tad bit harder to turn. Unless it is below zero, I do not think we are even going to be able to tell except for this message, and the fan being on high. My issue was a bit more complex, in that it happened when I wanted my A/C on, and my A/C quit working, and only hot air came out with the fan on high. When I disconnected the negative battery, my A/C worked immediately and the alert has not returned yet. Going on about a month now I think. Somehow the Thermostat is also tied to this issue, that I do not understand, but they say in this article, that you have to replace both of them to fix the issue. Another person or more thinks it is a bad battery connection. I am still doing research.
 

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I had the identical problem of 'steering assist reduced' with the temperature gauge dropping to zero and no A/C for over a week. I had my oil changed today and the tech stated that my battery was pushing out lower than normal voltage. The 'check engine light' was on for steering assist, but since I only had an appt for an oil change they did not address the issue. After reading various posts where removing the negative cable for a few minutes corrected the issue I tried it. (as well as cleaning the terminal) VIOLA! It is corrected and I saved an engine code fee in addition to a thermostat replacement. I will keep an eye on the temp gauge to see if it recurs. Bottom line: keep the battery terminals clean.
Is this still working for you? My battery posts seem ok, but I'm still having the same issues.
 

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I am not BOBT. but I am experiencing this issue as well. I am probably at about a month without the "steering assist" message since removing the negative terminal cable. I also cleaned the terminal with that wire brush tool they sell, and applied dielectric grease. I have read of another guy with about the same duration of "fix" about a month to 6 weeks. However, I also just replaced my battery. It turned out to be a failed starter, but MY attempt at fix was to replace the battery. I got the most powerful battery I could afford, because I read on this forum about low voltage being a potential source of these electronic issues. I read that autozone may tell you the battery is "good", but it is not "good enough" to keep all the gadgets we have on these well equipped SUVs working. So, my old battery that was "good" was 2 years old. I now have an additional measure of protection with a brand new battery. I hope to never see that steering assist message again. Hope you experience the same.
 

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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
It is located beside the thermostat under the air intake , my 2019 Acadia had this problem , I replaces the sensor , worked fine for 2 days and did it again , indicating that there may be another problem that's affecting the temp sensor , after more research and plugin in the laptop , the temp sensor was working as intended but discovered it could be a number of of other things, it could be the coolant temp sensor , could be the thermostat stuck open so the car thinks its running to cold , could also be the wiring harness or plug , , I am currently doing more research and will let you know once I find the root cause.
 

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I actually have a 2017 Acadia Denali and mine started doing this exact same thing about 6 months ago, but a couple days later, everything went back to normal. I read on this forum that the Coolant Temp Sensor was the main problem on the older models, so I went to the GMC dealer and purchased a new sensor. I figured I would wait until it problems happen again, and then change the sensor. However, the Acadia ran great all summer, until last week, the temp gauge dropped to 0, the air blew warm, the rad fan was racing, and the "Steering Assist is Reduced " warning came on the dash. I drove the car the next day and in the middle of my drive, everything started working again. Then last weekend, I finally had time to replace the Coolant Temp Sensor. It is not in the same place as everyone says for the older models. It took me 3 hours to find it, but I finally did and replaced it. It is actually on the top of the engine, left side under the air intake cover. I thought everything would be fine, but then today, all my problems came back. Now I'm puzzled, what is wrong with these that this problem keeps coming back? Do you think its the thermostat?
is located beside the thermostat under the air intake , my 2019 Acadia had this problem , I replaces the sensor , worked fine for 2 days and did it again , indicating that there may be another problem that's affecting the temp sensor , after more research and plugin in the laptop , the temp sensor was working as intended but discovered it could be a number of of other things, it could be the coolant temp sensor , could be the thermostat stuck open so the car thinks its running to cold , could also be the wiring harness or plug , , I am currently doing more research and will let you know once I find the root cause.
 

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This link has all the problems that may cause the issue of the temp sensor in a holden arcadia of cold gauge , fans running , aircon not working and the screen will show steering Assist reduced ,
 

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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
One month and about 1000 miles after my repairs and no more of the various issues... this is looking like a LONG TERM fix. Close to calling it "SOLVED", at least for me
 

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I went through all 8 pages of this thread and not 1 person has posted the same results as I have in another thread. The thermostat and sensor has not been the problem in my Acadia since my scanner reads coolant temp but my dash does not. So the temp sensor works and the thermostat opens and closes according to a 6+hr road trip of monitoring everything. I force commanded my AC clutch on so I could have AC for the remainder of our trip and still had no issues with temp especially since my HD cooling fan I installed was commanded at 80%. Resetting the computer has fixed the communication issue between the temp sensor and the instrument cluster and still to date have not had a sensor issue only a communication issue. last time I reset the battery it lasted a month so the issue should come back in the next week or so. I will post how my scan tool reads temp but the cluster will show 0 temp proving a communication error not a mechanical issue or sensor issue. Stay Tuned!!!!!
 

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I went through all 8 pages of this thread and not 1 person has posted the same results as I have in another thread. The thermostat and sensor has not been the problem in my Acadia since my scanner reads coolant temp but my dash does not. So the temp sensor works and the thermostat opens and closes according to a 6+hr road trip of monitoring everything. I force commanded my AC clutch on so I could have AC for the remainder of our trip and still had no issues with temp especially since my HD cooling fan I installed was commanded at 80%. Resetting the computer has fixed the communication issue between the temp sensor and the instrument cluster and still to date have not had a sensor issue only a communication issue. last time I reset the battery it lasted a month so the issue should come back in the next week or so. I will post how my scan tool reads temp but the cluster will show 0 temp proving a communication error not a mechanical issue or sensor issue. Stay Tuned!!!!!
Thanks for this post. I was about to pull the trigger on those parts. I think I will hold off now. Has your issue resurfaced?
 

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Thanks for this post. I was about to pull the trigger on those parts. I think I will hold off now. Has your issue resurfaced?
It did today. I was so excited to hurry up and get home to really dive into it. When I got in with my scanner everything was working fine. So I was actually pissed it was working. Hopefully soon it will come back. One fault I get with this issue is a can bus signal low to BCM. But the ECT is through the ECM so not sure what that has to do with it yet.
 

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I still keep wondering if there is another temp sensor that is unknown or if the ECT signal also enables a "virtual" temperature signal that is utilized somewhere else in the ECM/BCM interconnect and operation.
Either that or a break in the signal or communication interruption in the process.

I seem to recall reading that one of the earlier Acadia ( or Traverse?) model years had two temperature sensors. But maybe I've read and been on too many automotive forums. . . ?
 

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I still keep wondering if there is another temp sensor that is unknown or if the ECT signal also enables a "virtual" temperature signal that is utilized somewhere else in the ECM/BCM interconnect and operation.
Either that or a break in the signal or communication interruption in the process.

I seem to recall reading that one of the earlier Acadia ( or Traverse?) model years had two temperature sensors. But maybe I've read and been on too many automotive forums. . . ?
Yeah I wanted to put my process meter on the temp sensor and see what it's output was but unfortunately everything was working by the time I got home. Hopefully soon it will stay not working long enough for me to run through it. I have not seen any other sensor for coolant on my scanner or when looking up parts. Even talking at work, since we are all instrumentation technicians, it seems to be a communication issue more than a mechanical issue. I wanted to make a short video today showing the temp reading in and the cluster showing 0. Maybe soon.
 

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Yeah I wanted to put my process meter on the temp sensor and see what it's output was but unfortunately everything was working by the time I got home. Hopefully soon it will stay not working long enough for me to run through it. I have not seen any other sensor for coolant on my scanner or when looking up parts. Even talking at work, since we are all instrumentation technicians, it seems to be a communication issue more than a mechanical issue. I wanted to make a short video today showing the temp reading in and the cluster showing 0. Maybe soon.

Finally got it to happen again. Of course not at home but was able to document my scanner reading it and it not displaying on the cluster.
 

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It too me looks like NOT the ETS or thermostat. I have great heat but no gage and in my temps it would be warm air at best and most here say they changed them and it still comes back. I changed the battery it was 4 years old anyway and it went away and came back, probably the negative battery terminal reset. The lady scanned it and ofund NO codes?. I have noticed the coolant was down to the lower bowl maybe 10oz? not sure where it went but could be burning it none in the oil. I topped it off i will monitor.

I have NOT done a reflash but there is a company 2017 GMC Acadia 3.6L Engine Computer (PCM/ECM/ECU) Plug&Play - MINTT that sends a new ECM flashed for $175 wondered if this might be a option my dealer wants close to that to reflash the OEM that might not be good anyway.

Anyway hoping something definitive shows up i hate to hear of all the people replacing good thermostats and sensors and have a reoccurring issue i would be livid. A open themostat in cold weather would not give good heat and would stay stuck not unstick with a battery cable removal this is a electrical/ECM/Bug issue i am sure
 

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Yeah mine intermittently comes and goes. Will show up at start up and go away while driving, or drop while driving and come back after a couple start ups. I always get a low can bus signal everytime it happens too.
This sounds pretty troubling.
So you haven't been able to nail down a cause for this occurring other then that it is some sort of electrical gremlin?
Pardon . . I understand what CANBUS is. . . but what is a canbus low condition? A communication problem on it?
 

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This sounds pretty troubling.
So you haven't been able to nail down a cause for this occurring other then that it is some sort of electrical gremlin?
Pardon . . I understand what CANBUS is. . . but what is a canbus low condition? A communication problem on it?
Correction:
Serial Data Gateway Module; code U0078-00
Control Module Communication Low speed CAN BUS off
 

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Correction:
Serial Data Gateway Module; code U0078-00
Control Module Communication Low speed CAN BUS off
Thanks for the detail.
I see other GM cars and trucks have had the same issue.
In some cases, it was the T-stat.
In others apparently not.
I blame it on an over complicated mess what with all the modules "checking in" and having to chat over that internal vehicle network.
More and more it's sounding like some intermittent connection somewhere or. . . . just some coding error or timing error in the data. But why would the engine coolant temperature data have to be so glitchy then ?
Such a pricey and pain in the butt job to replace that T-stat and/or ECT sensor only to find out they are not the problem.
 
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