# 2015 GMC 2500 HD Engine braking?



## Motorman 007 (Jan 11, 2005)

My '15 GMC appears to have some form of engine braking. In researching this I thought only the Duramax had engine braking. Does the 6.2 with the 6 speed auto have this feature? It is not in tow haul mode.....


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## Cosmic Charlie (Feb 1, 2009)

http://www.gmc.com/sierra-2500hd-pickup-truck/build-and-price.html?x-zipcode=01985

both these options are listed as FREE, just check them off when ordering, says Duramax is required for the Exhaust Brake

Engine exhaust brake

Reduces the amount of conventional braking needed while towing a heavy trailer or driving downhill
Uses the variable vanes in the turbocharger to smoothly and quietly create additional back pressure in the engine to help slow the vehicle
Works with the Allison® transmission's Tow/Haul mode and Auto Grade Braking to help the driver maintain the desired speed even on long, steep downgrades
Requires the available Duramax® 6.6L Turbo-Diesel V8 engine

Hill Descent Control

Included with the awe-inspiring Z71 Off-Road Suspension Package, Hill Descent Control:

Uses antilock braking to help provide a smooth, controlled descent in rough terrain
Activates by pushing a button on the instrument panel
Works without the driver pressing the brake pedal
Included in the available Z71 Off-Road Suspension Package


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## cubicinches (Oct 19, 2008)

The 6.0 gassers have hill descent control. It's not engine braking, but as was stated above, it uses the anti-lock braking to automatically assist in braking when towing and such.


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## JustJeff (Sep 9, 2009)

Rams have had it for a couple of years as well on their diesels.


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## Motorman 007 (Jan 11, 2005)

Cosmic Charlie;1900811 said:


> http://www.gmc.com/sierra-2500hd-pickup-truck/build-and-price.html?x-zipcode=01985
> 
> both these options are listed as FREE, just check them off when ordering, says Duramax is required for the Exhaust Brake
> 
> ...


I have the Z71 package and the hill descent control, however, that function is selectable via a dash mounted switch. The switch is not activated and the icon on the dash is not lit. Does anyone know if this new 6 speed tranny is an Allison behind the new 6.2 gasser?


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## cubicinches (Oct 19, 2008)

Motorman 007;1901812 said:


> I have the Z71 package and the hill descent control, however, that function is selectable via a dash mounted switch. The switch is not activated and the icon on the dash is not lit. Does anyone know if this new 6 speed tranny is an Allison behind the 6.2 gasser?


I'm not aware of a 6.2 being available in a 2500... only a 6.0. And the 6.0 uses a 6L90 transmission, not an Allison.


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## Motorman 007 (Jan 11, 2005)

cubicinches;1901813 said:


> I'm not aware of a 6.2 being available in a 2500... only a 6.0. And the 6.0 uses a 6L90 transmission, not an Allison.


You're correct (again) CI. The 6.2 420HP is only available in the half ton (doesn't make sense to me...) and mine is a 6.0.
I found my answer. The feature is called "Powertrain Grade Braking" and is standard on all of the 6 speed trannys. It can be disabled by holding the tow/haul button for a few seconds but you would have to do that every time you cycle the ignition. It activates when you apply the brake even on the slightest grade, automatically downshifts the tranny to the next lowest gear and holds that gear as you slow to a stop. Now that I know what it is and how it works, I need to play with it a bit....


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## cubicinches (Oct 19, 2008)

Motorman 007;1901830 said:


> You're correct (again) CI. The 6.2 420HP is only available in the half ton (doesn't make sense to me...) and mine is a 6.0.
> I found my answer. The feature is called "Powertrain Grade Braking" and is standard on all of the 6 speed trannys. It can be disabled by holding the tow/haul button for a few seconds but you would have to do that every time you cycle the ignition. It activates when you apply the brake even on the slightest grade, automatically downshifts the tranny to the next lowest gear and holds that gear as you slow to a stop. Now that I know what it is and how it works, I need to play with it a bit....


I rode to the dealership, about an hour west of me last night, with a friend who was picking up his new 2500HD gasser. On our ride home, we were commenting that it would be nice if they would put the 6.2 in the 2500s.

Interesting info on the powertrain grade braking feature. I'm going to pass that info on to my buddy. We were playing around with the hill descent control a little bit on the ride home. I wasn't certain on it's operation, as my 2015 is a Duramax.


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## Cosmic Charlie (Feb 1, 2009)

cubicinches;1901835 said:


> On our ride home, we were commenting that it would be nice if they would put the 6.2 in the 2500s.


I read somewhere the 6.0 gas has HD 6 bolt mains vs the regular duty 6 bolt mains in the 6.2. (thought I don't know this as a fact).

Also the 6.2 is a $2000 option in the 1500 vs the 2500 is about $3000 more than the 1500. Dollar for dollar the 2500 is a better deal (in my book) - much more upgraded parts . GM keeps the price down by Mass Production and the 2500 is built just as a 1 gas or 1 diesel (more or less).

I agree more variety is better, but the number of 2500's vs 1500's built hardly compare ... so less variety ...


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## Cosmic Charlie (Feb 1, 2009)

Cosmic Charlie;1902060 said:


> I read somewhere the 6.0 gas has HD 6 bolt mains vs the regular duty 6 bolt mains in the 6.2. (thought I don't know this as a fact).


From GM :

The standard engine on all Silverado HDs is a 6.0L Vortec gas V-8 with continuously variable valve timing, matched with a six-speed automatic transmission. It is rated at 360 horsepower and 380 lb-ft of torque on 2500 models,* and is specifically engineered for low-end torque.* A version rated at 322 horsepower is standard on 3500s. Pickups with either version are E85 FlexFuel capable.


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## sargex595 (Oct 11, 2005)

I have a 2013 GMC 2500HD with the 6.0 and it does the same thing. Mine seems to apply by just letting off the gas without applying the brakes. I have to watch it when on the interstate as it really slows you down. Still trying to figure it out.

Curt.


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## Motorman 007 (Jan 11, 2005)

sargex595;1902964 said:


> I have a 2013 GMC 2500HD with the 6.0 and it does the same thing. Mine seems to apply by just letting off the gas without applying the brakes. I have to watch it when on the interstate as it really slows you down. Still trying to figure it out.
> 
> Curt.


That's exactly what my '15 does. It doesn't have to be on any kind of a grade either....


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## snowymassbowtie (Sep 22, 2013)

My 2009 gmc 2500 HD has it too


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## Cosmic Charlie (Feb 1, 2009)

On my 11 - when I rolling up to a stop sign, as the truck downshifts thru the gears, the computer will slightly bump up the rpm's (give a bit of throttle) to make is smooth out -

I'd call it rev match built into the drive trane system ...


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## 82k10ny (Nov 30, 2014)

Cosmic Charlie;1902283 said:


> From GM :
> 
> The standard engine on all Silverado HDs is a 6.0L Vortec gas V-8 with continuously variable valve timing, matched with a six-speed automatic transmission. It is rated at 360 horsepower and 380 lb-ft of torque on 2500 models,* and is specifically engineered for low-end torque.* A version rated at 322 horsepower is standard on 3500s. Pickups with either version are E85 FlexFuel capable.


the part that boggles my mind is if you go to gms web site a 5.3 in a 4wd pickup is rated 355 hp at 5600 rpm 383 ftlbs at 4100. a 6.2 in a 4wd 1500 is rated 420 hp at 5600 460 ftlbs at 4100 rpm

then a 6.0 in a 2500hd 360hp at 5400 rpm and 380ftlbs at 4200 rpm.

so a 5.3 is 5 hp less at 200 rpm more and 3 ftlbs more at 100 rpm less... so in all reality what the hell is the point in the 6.slow anymore. might as well just re tool the 5.3 bottom end to be a little more stout and put a rv tune in it for the 2500s so your 1500 line is the 355/383 the 2500 version of the 5.3 is say 375/400 (easily doable im sure) then the 6.2 would be your denali motor. just makes sense the 6.0 is like a 305. worthless in everyway except a boat anchor. 
and i love gm but sometimes there logic is so ford( arse backwards) my head spins


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## Rick547 (Oct 9, 2009)

82k10ny;1905421 said:


> the part that boggles my mind is if you go to gms web site a 5.3 in a 4wd pickup is rated 355 hp at 5600 rpm 383 ftlbs at 4100. a 6.2 in a 4wd 1500 is rated 420 hp at 5600 460 ftlbs at 4100 rpm
> 
> then a 6.0 in a 2500hd 360hp at 5400 rpm and 380ftlbs at 4200 rpm.
> 
> ...


Without seeing a dyno chart it is hard to tell. The 6.0 may have more usable torque at a lower rpm than the 5.3. I guess I need to look it up.


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## jerpa (Feb 4, 2014)

Rick547;1905556 said:


> Without seeing a dyno chart it is hard to tell. The 6.0 may have more usable torque at a lower rpm than the 5.3. I guess I need to look it up.


^Yup.

Substantially more torque available below 3000 RPM. It produces 300lb/ft almost at idle. Personally I'll take the "old school" cast iron block, proven reliability of the design, and low end grunt over a few more high rpm HP or lb/ft.


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