Exhaust brake operation

[DenaliDrew]

Hi folks, as I'm in Colorado, I do a lot of mountain passes in my 21 Denali XL with the 3.0 duramax. There is not a lot of documentation as to how the exhaust brake works, nor any indication that it is in operation. What does everyone know about that topic? Do you just turn it to Tow mode and call it a day?

 

[DenaliDrew]

More specifically, to jog some conversation perhaps, here's my concern - for example, when I'm coming down the hill from the Eisenhower Tunnel into Summit County Colorado - about a 3,000 foot drop over maybe 10 miles, I'll put it in cruise control in Tow/Haul mode. You can feel the RPMs spike as the transmission downshifts, but at times it revs so high I feel like I'm at risk of damaging the engine. Researching it a bit, it appears the engine has a higher redline in these braking scenarios vs. a true acceleration scenario. Anyone else experience this? Like 3,750 rpm or higher. Safe?

 

[Pro299]

I've noticed on downhill grades that if I use ACC rather than regular cruise control, it will stay within three or so miles per hour of the set point. I don't use tow/haul unless I'm actually towing. The calibration for shift points and RPMs will be significantly longer and higher than normal. Having said that, unless you're getting into the redline on the tach which is over 5k on the DMax, no biggie.

 

[RIZE_UP]

Hi folks, as I'm in Colorado, I do a lot of mountain passes in my 21 Denali XL with the 3.0 duramax. There is not a lot of documentation as to how the exhaust brake works, nor any indication that it is in operation. What does everyone know about that topic? Do you just turn it to Tow mode and call it a day?

In tow haul mode on 22 burb, says exhaust brake on and when you switch modes says on screen exhaust brake off. I don't have any mountains in South Texas. When I pull my 3800lbs trailer, I do slightly feel a drag on the motor like the exhaust brake is working. It is nothing like my ram 3500 ** Cummins though...lmao

 

[Larsonxjs]

3,750 is a good number haha. That’s when the engine is making its 277 hp and the torque curve is falling off

 

[DenaliDrew]

Ok, thanks. I guess I won't worry about it revving high. I assume the engine will limit itself to a safe RPM. Although I like getting a zillion mpg by putting it in neutral as well if not towing anything. Interesting that the burb has an indicator. If the 21 yukon has it, I sure haven't seen it. I saw an interesting video with a GM engineer on the 3.0 talking about how they wanted to make a light duty diesel easy and there wasn't a lot of room on the dash for another switch, so they made it automatic instead.

 

[MooseBrute]

Hi folks, as I'm in Colorado, I do a lot of mountain passes in my 21 Denali XL with the 3.0 duramax. There is not a lot of documentation as to how the exhaust brake works, nor any indication that it is in operation. What does everyone know about that topic? Do you just turn it to Tow mode and call it a day?

You put it into Tow Haul mode at which time you will see messages that exhaust brake is on
Then after that on my Tahoe 2022 I find it does nothing whatsoever.
My Chev dealer mechanic took it for a test ride down a 10% hill and confirmed yes it will not work at all

He was going to call General Motors if he can ever get through to them
And he says I don’t have an exhaust brake in the first place
General Motors are full of themselves

Mine won’t down shift or nothing unless I do it manually myself out of tow haul mode

Still no reply from anyone after a week

Not only that the mechanic says he does know of any one that has a 3.0 that works

Every one of them are calling in saying theirs won’t work at all

Final results will be General Motors doesn’t give a rats ass

And we can all stop bothering them

if it ever gets fixed I’ll post it in here
But fat chance of that seeing as it really isn’t an exhaust brake in the first place

General Motors just calls it that to get us to buy their crap

In the meantime I’ll put it in manual and shift myself
GM did a play on words better known by some as false advertising or embellishing or just plain old story telling it BS.

 

[UsualSuspect]

I asked my mechanic about it. He took a look and said GM is using a variable vain turbo, and that is essentially an exhaust brake if the vains are moving as they should. He said not expect too much, it isn't going to provide anything near the exhaust braking on the 6.6, Detroits, or Cummins. As he put it, it's a light duty version.
He also said if you are not towing, don't expect it to do much of anything, it varies the braking by load. To engage it you have to use the brakes, and the heavier, the faster the slowdown.
I don't haul anything with mine, so I can't tell you if it does or doesn't work, I have a 2500HD with a 6.6 I use for towing.

 

[steiny93]

Wife has a 2021; I've towed with it a few times and I've had it in the mountains a fair number of times.

On hers
It behaves differently in tow/haul vs regular.
Going down a grade, in tow/haul if you force downshifts the vehicle slows much more aggressively then if you aren't in tow/haul mode.

But...
It doesn't force downshifts nearly as aggressively as I'd like (if you don't force them via the -/+ on the dash) as say the 6.6 or 6.7's; but perhaps that is intentional for the target audience.

In addition, the behavior where you brake then the exhaust brake kicks in doesn't exist on the 3.0 (DMax or EcoDiesel).

When not towing using tow/haul on grades and forcing a downshift via the -/+ on the dash will hold the vehicle to lower speeds at lower rpm then without tow/haul activated. Which seems to indicate the powertrain is doing something different between the modes.

 

[Doubeleive]

my 12 uses the transmission to help brake, not sure why they would take that feature away even on a diesel