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when my 2021 Denali changes to 4 cly mode I get what is best described as a vibration or rumble sound. everything is good in the 6 cyl mode. Is this a normal operation or should I take it in.
 

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I would take it in. It could be anything from low on transmission fluid from the factory to a torque converter clutch acting up.
 

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I do find (my '19 has no V4 vs V6 display so I have no proof) that when in V4 mode it does feel a bit more rough (as 4 cylinders do). Nothing bothersome...
I wonder if there's an aftermarket display unit that shows when you're in V4 or V6 mode...
I wonder almost more if there's a Range unit now that disables the AFM V4 mode.
 

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My 2020 (V6 with 1400 miles)has developed a low vibration/rumble when at idle RPM in park or in drive. I will be taking it in because a new car should not sound that way and it is annoying to me. I will have to see if it is in 4 cyl mode when the issue occurs.

I have turned off the AC/defrost and anything else I can think of and the issue persists.

Keep us posted if you do take it in and I will do the same (unfortunately it will not be until after Christmas).
 

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AFAIK it should never go into 4 cylinder mode at idle, only under low load and specific conditions.
 
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Correct... . the engine will only go into V4 mode with the vehicle in gear and moving. usually it will go into V4 mode when driving at a steady speed and even up some gentle inclines. I've seen it in V4 mode on the DIC from anywhere between 25 to 70 MPH. Rarely drive faster than that.
A slight pressure on the gas pedal to speed up a just a bit and it will go back into V6 mode.
The above is pretty much also true of my 2017 Colorado with the same 3.6L V6 engine but has an 8 speed transmission. Although, it does not go into V4 mode often or for too long.
I have not observed any untoward vibration at idle, low speeds or any other scenario. Barely discernable to feel or hear when it does go in or out of V4 mode.
 
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when my 2021 Denali changes to 4 cly mode I get what is best described as a vibration or rumble sound. everything is good in the 6 cyl mode. Is this a normal operation or should I take it in.
GM says its normal but i think its a defect, i hate it. I took my 2020 denali in twice and they say its normal, I cant stand the dronning sound, when i bought this SUV i bought it because of the 6 cyl. had no idea it droped to 4cyl. So disapointed.
 

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I do find (my '19 has no V4 vs V6 display so I have no proof) that when in V4 mode it does feel a bit more rough (as 4 cylinders do). Nothing bothersome...
I wonder if there's an aftermarket display unit that shows when you're in V4 or V6 mode...
I wonder almost more if there's a Range unit now that disables the AFM V4 mode.
I checked and Range does not make one for my 2020 acadia. I would of gladly paid 300 bucks to keep it in 6 cyl. mode.
 

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GM says its normal but i think its a defect, i hate it. I took my 2020 denali in twice and they say its normal, I cant stand the dronning sound, when i bought this SUV i bought it because of the 6 cyl. had no idea it droped to 4cyl. So disapointed.
I'm wondering if things have changed with the 2020 and 9 speed transmission. Perhaps the engine RPMs are being kept lower than in the 6 speed.
If you notice "droning". .. maybe ask to have the Active Noise Cancellation system checked out.
With Our 2019, I have never heard any kind of drone or any other annoying sounds, vibrations, or rumbles.
Our 2019 is very quiet. The actual shifting could be smoother. Shift points do not seem optimum for a smooth driving experience at times.
 

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I checked and Range does not make one for my 2020 acadia. I would of gladly paid 300 bucks to keep it in 6 cyl. mode.
Agree. I checked with them soon after buying my Acadia last year. They did not, still not, but I'm almost considering buying one for a Canyon to see if it'll work.
I partly just don't like the idea, do feel like it's rough in 4 cyl mode, and don't really care about gas mileage.
 

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The dealership let me try a 2021 denali and it was the same as my 2020, the noise is like when you have a back window down but really low frequency drives my ears crazy.They say its normal to do that when it goes to 4cyl. i say its ********.
 

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I noticed it on my 2020 and the 2 others I test drove. I think it is normal. It was more of a noise like when you lug a car with a standard transmission. Very narrow band of RPM and Speed when I felt it.
 

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OK, I have nothing remotely like that. Mine is barely noticeable and rare. Nothing audible, just a slightly rough (4 cyl feel) every so often.
Edit; guessing the newer ones are a combination of 4 cyl mode and too many tranny gears to choose from (compared to my mere 6).
 
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I've never noticed it on my '18 SLT. Unless I'm staring at the DIC, I can't tell when it swaps between 4 and 6.

My son had cylinder deactivation tuned out of his SS Camaro. Drawback is it mucks with your warranty.
 

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when my 2021 Denali changes to 4 cly mode I get what is best described as a vibration or rumble sound. everything is good in the 6 cyl mode. Is this a normal operation or should I take it in.
Where does your Denali display cylinder cycling for AFM? Previous model year C1XX-platform Acadia Denalis didn't have a display for it. AFM cylinder cycling is only visible in the AVE/BEST mpg page of the DIC on my XT5.

I've noticed some droning/rumbling while cruising on fresh asphalt-paved highway. It's gone away in some distance or when I've switched lanes. Checked the display page when it happened and the vehicle was almost always in 6-cylinder mode. I've attributed it to differing frequencies of vibrating rollers used to compact the asphalt. Never have noticed anything like that on concrete-paved roads.
 

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I noticed it on my 2020 and the 2 others I test drove. I think it is normal. It was more of a noise like when you lug a car with a standard transmission. Very narrow band of RPM and Speed when I felt it.
I do also feel it. Both the drone and vibration are extremely slight and almost unnoticeable. It is displayed right on the main screen as if it is proud to say you are in V4 mode.

I think this is going to be one of those things some people are more sensitive to. All 3 vehicle I test drove seemed identical. And at highway speeds I did not notice it at all. Much more noticeable at lower speeds.
 

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My 2020 SLE shows 4 or 6 cyl on the DIC in the Fuel Economy Mode. The "droning" sound I hear may be at different times than the OP and it may just be my expectations of it being quieter than it is. (its very quiet when driving). I don't drive it much since its my wifes vehicle but when I do I notice it and I don't remember hearing it when we first bought it.
 

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...
I think this is going to be one of those things some people are more sensitive to. ...
You may be right. It's a lot like when 8-6-4 DOD (displacemrnt on demand) was introduced by Cadillac. Cylinder cycling on that was hated by many - liked by many. Then, it wasn't a case of driver 'sensitivity' to it. The cylinder cycling was definitely noticeable. One thing cool about that system was that it could be locked in any mode with a few key presses on the climate control.
 

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OK, I have nothing remotely like that. Mine is barely noticeable and rare. Nothing audible, just a slightly rough (4 cyl feel) every so often.
Edit; guessing the newer ones are a combination of 4 cyl mode and too many tranny gears to choose from (compared to my mere 6).
Agree. . . our 2019 Acadia SLT-1 with V6 has nothing audible and no low frequency drone or rumble.
That makes me wonder if something was changed in the ANC system or perhaps the new 9 speed and V4 mode produces some harmonics and the ANC isn't addressing them as well.
 
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Back in 2017 had a similar deal. rough/ vibration around 1500-1600 rpm. I had a TSB about it which denied existed. There’s another member on here had the same problem. Long story short, they reprogrammed the PCM. It went away. Good ever since. Perhaps Speleos remembers, her screen name was something like allboys.
 
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