PWM Sweep Noise when in Auto or 4WD

[tbully]

Hello All -

Brand new 2015i Denali owner here.

We have a little snow in the Detroit area tonight so I had the chance to try out AWD / 4x4. I thought about putting this in the drivetrain section but I think it's more of an electronics issue.

First, I have very sensitive hearing and am lucky (?) enough to be able to hear well at the top of human range.

I noticed when in Auto or full-time 4x4 there is a strange PWM sweep noise coming from behind the instrument panel when varying throttle input (cruise also does it).

You can also create the noise by simply sitting in park and switching to Auto or Fulltime.

It's a faint squeeling noise - similar to the horizontal / fly-back section of older TVs.

Anyone else have this? Super annoying!

Thanks.

 

[motorwerks]

Hmmm...nothing like that on my 2015i...I'm pretty sensitive to noises too. I'll take a better listen tomorrow.

 

[tbully]

Thanks. I'm hoping you don't have it so it can be a repairable condition. Things like these are usually design flaws though. Maybe Mr. White (our resident electronics expert) will chime in. It's way up there. 12-14 KHz. But I hear it no problem! Ugh!

 

[tbully]

Found this thread that points to a transfer case control module. Interesting. http://www.tahoeyukonforum.com/forum/showthread.php?t=61843

 

[hosseface]

Hello All -

Brand new 2015i Denali owner here.

We have a little snow in the Detroit area tonight so I had the chance to try out AWD / 4x4. I thought about putting this in the drivetrain section but I think it's more of an electronics issue.

First, I have very sensitive hearing and am lucky (?) enough to be able to hear well at the top of human range.

I noticed when in Auto or full-time 4x4 there is a strange PWM sweep noise coming from behind the instrument panel when varying throttle input (cruise also does it).

You can also create the noise by simply sitting in park and switching to Auto or Fulltime.

It's a faint squeeling noise - similar to the horizontal / fly-back section of older TVs.

Anyone else have this? Super annoying!

Thanks.

Yup. Few people seem to be able to hear this but you are hearing the same thing I was. Your link to my thread will fix you up.

The TCM is right above the accelerator to the right. It just pops in. Pop it loose, wrap it (BURY IT!!!) inside acoustic foam and the noise will be gone for good!

Once you hear that noise it drives your crazy,

 

[tbully]

Confirmed. Stuffing a towel up there temporarily has muted it somewhat. This isn't safe to drive with obviously so I just tested it in the garage.

Mind snapping a picture of your job?

 

[hosseface]

Confirmed. Stuffing a towel up there temporarily has muted it somewhat. This isn't safe to drive with obviously so I just tested it in the garage.

Mind snapping a picture of your job?

Sure. I'll get you one.

Not much to see honestly - I just wrapped it up in the foam and put some duct tape around it to keep the foam on there.

FWIW - probably going to be some haters on this but it works. I can hear it now: "what a rig on a 70K vehicle" Good luck getting the dealer to replace the TCM and either not:
A)Get your truck beat up
B)Create a new problem while they're at it
C)End up with the infamous Service 4X4 message
D)Have the new module make the same exact noise

 

[revengejr]

You're not alone. Help!

I just posted this on another thread but just saw this. Here is our problem:
We just leased a 2015 1/2 Tahoe LT. My wife started complaining of a high pitched noise coming from the dash on the left side but I couldn't hear it. We took it back the dealership and they couldn't hear it either, until my wife convinced them to have their receptionist sit in the car and she immediately heard it. The dealership immediately swapped us to an identical new Tahoe since we had just picked up the car less than 48 hours earlier and their service manager said he can not fix something he can not hear. (very accommodating dealer) New truck had no noise...until while playing around with settings, my wife turned the 4wd selector knob from Auto (which was set from the factory) to 4wd. The high pitch noise came back. Now, unless she keeps the knob on 2wd, she hears noise on Auto or 4wd, effectively making our new truck a rear-wheel drive car. I did some testing with a sound meter and tone generator. The sound is somewhere around 15kHz at about 44db, which is loud - if you can hear it. Think a train passing relatively close by but ear-piercing. I apparently can't hear tones above 14,600Hz and when I tested several colleagues using a tone generator, generally everyone over the age of 40 couldn't hear any tones above 14,800Hz, however a few young women in my office could hear tones above 15kHz. A quick Google search verified that in fact this is a normal, previously known fact that young women can hear very high pitched tones older women and most men can not hear. Go figure. Now, we have a brand new Tahoe on a 39 month lease we just got that we can't take out of 2wd since it causes my wife to get a serious headache. Is this the same thing you were hearing? If so, what was the fix? Replacing that part? The idea of wrapping a leased car's parts in foam may not go so well. The dealership says they've never heard of this and want to bring someone from GM in to have at it. It seems to be coming directly from the selector knob or something immediately behind it. Any advice or suggestions would be immensely appreciated! Thanks!

***EDIT
It's also worth mentioning she hears the noise even while going at 2mph or 60mph as long as she is depressing the accelerator. Doesn't matter the speed.

 

[Anon2015]

Ok...I don't hear it in mine but; what the heck, I'll pull out a mic and see what gives...

In my 2015i Denali I get a 21dB SPL spike at 14785Hz when shifting between any mode (2WD, Auto, Hi, Low). It is momentary during the initiation of the shift and does not continue. Again, instantaneous only. (It is long enough for Sonar to find you and kill you; but, I don't believe that is an issue in this case.


In the case of Hosseface and I, one of the two of us has a faulty TCM.

 

[hosseface]

I just posted this on another thread but just saw this. Here is our problem:
We just leased a 2015 1/2 Tahoe LT. My wife started complaining of a high pitched noise coming from the dash on the left side but I couldn't hear it. We took it back the dealership and they couldn't hear it either, until my wife convinced them to have their receptionist sit in the car and she immediately heard it. The dealership immediately swapped us to an identical new Tahoe since we had just picked up the car less than 48 hours earlier and their service manager said he can not fix something he can not hear. (very accommodating dealer) New truck had no noise...until while playing around with settings, my wife turned the 4wd selector knob from Auto (which was set from the factory) to 4wd. The high pitch noise came back. Now, unless she keeps the knob on 2wd, she hears noise on Auto or 4wd, effectively making our new truck a rear-wheel drive car. I did some testing with a sound meter and tone generator. The sound is somewhere around 15kHz at about 44db, which is loud - if you can hear it. Think a train passing relatively close by but ear-piercing. I apparently can't hear tones above 14,600Hz and when I tested several colleagues using a tone generator, generally everyone over the age of 40 couldn't hear any tones above 14,800Hz, however a few young women in my office could hear tones above 15kHz. A quick Google search verified that in fact this is a normal, previously known fact that young women can hear very high pitched tones older women and most men can not hear. Go figure. Now, we have a brand new Tahoe on a 39 month lease we just got that we can't take out of 2wd since it causes my wife to get a serious headache. Is this the same thing you were hearing? If so, what was the fix? Replacing that part? The idea of wrapping a leased car's parts in foam may not go so well. The dealership says they've never heard of this and want to bring someone from GM in to have at it. It seems to be coming directly from the selector knob or something immediately behind it. Any advice or suggestions would be immensely appreciated! Thanks!

***EDIT
It's also worth mentioning she hears the noise even while going at 2mph or 60mph as long as she is depressing the accelerator. Doesn't matter the speed.

Mine was the same way. I posted in your other post about this...listen to the right above the accelerator pedal and see what happens. Stick your head down there and have a second person operate the knob. To actually locate the noise on mine in the first place, I used a product called Steelman Engine Ears. It is an electronic stethoscope with a mic on it and a pair of headphones that really picks up noises. It showed right up with that.