Grade breaking

Daddyz · September 10, 2021

Hello all , I have a 2017 GMC Savana and while driving on a levelled roar without pulling anything , and at about 60-80 Km , the “grade braking “ comes on .

Push the trailer button and it goes off .

Any ideas why this is happening ?

Thank you .

pokismoki · September 10, 2021

hold tow haul button for 6 seconds to disable it

Grumpy Bear · September 10, 2021

These are electronically controlled transmissions. That speed is about the threshold speed for the TCM comanded 6/5 downshift. Keeps her from lugging. It's quite normal and not part of Grade Braking.

Grade braking happens in cruise control when the down hill gravity speeds the Van a few MPH or KPH past the Cruise set point to HOLD the set point...or close to it. Keeps you from burning up your brakes and helps avoid speeding tickets. I think they still give those out.... :wtf:

That said as pokismoki notes...6 seconds to disable it on the tow/haul button. It resets itself each key cycle to on. You will get a message on the DIC when you've held it in long enough.

pokismoki · September 11, 2021

grade braking occurs on my truck going downhill , over 50mph i'm guessing, and i have depressed the brake pedal down for 30-60 seconds or longer, then you will feel an extreme downshift. I really dislike it, and know how to down shift manually

the 6l80e once downshifted into 2nd gear on me while i was going downhill on the grapevine at about 70mph, i was gently riding the brake pedal for awhile, then ******'n Whamm, got 2nd gear at 70! like WTF just happened ... thats when i left a brown staine in my undies. unreal who's the jerk at GM who programmed that ****** in! Now I always disable that crap as soon as i start herup

Grumpy Bear · September 11, 2021

With Peppers 3.23 gear 70 mph in 2nd gear is 6K rpm.

Well over her WOT shift point.

:rolleyes:

CamGTP · September 11, 2021

3.42's would max out before 70mph for 2nd gear, more like 58-60mph at redline.

I good rule of thumb with those gears is that it's a shift every 30ish mph.

pokismoki · September 11, 2021

8 hours ago, CamGTP said:

3.42's would max out before 70mph for 2nd gear, more like 58-60mph at redline.

I good rule of thumb with those gears is that it's a shift every 30ish mph.

is it possible to remove this in the software using HPtuners, where would i find these tables to delete the "grade breaking?"

CamGTP · September 11, 2021

I've never found a specific table for grade braking, so I am not totally sure.

Daddyz · September 11, 2021

Sorry , I'm aware how the system works , but ,still , I have not got an answer for my question .

Thanks

CamGTP · September 11, 2021

I guess your question is not very clear then.

Grade braking has a reason for coming on when slowing down. But if your problem has nothing to do with slowing down and you are at steady speed while still on the throttle, then something like that would likely require a scan tool hooked up to the van while driving to monitor that feature. Perhaps a dealership would have seen this problem before if that is the case.

I've driven plenty of Penske rental trucks that are GMC vans for work when one of our trucks are down and the only time I've seen the message come on was while slowing down.

Daddyz · September 13, 2021

Thanks CamGTP , very much appreciated , I will do that

Daddyz · September 15, 2021

Thanks CamGTP , very much appreciated , I will do that .

Also , is there a "level sensor " to detect the angle of the vehicle and if so , where would it be ..... Thanks again

pokismoki · September 25, 2021

On 9/15/2021 at 11:56 AM, Daddyz said:

Thanks CamGTP , very much appreciated , I will do that .

Also , is there a "level sensor " to detect the angle of the vehicle and if so , where would it be ..... Thanks again

it located in the DIC cluster under offroad , its not very accurate.

JimCost2014 · September 25, 2021

Normal mode powertrain grade braking assists when driving on a downhill grade to help maintain desired vehicle speed by using the engine and transmission to slow the vehicle. The mode helps reduce brake temperatures and wear on the traditional braking system. Normal mode powertrain grade braking defaults to “ON” after each ignition key cycle. To disable or enable all grade braking within the current ignition key cycle, press and hold the Tow/Haul button for three seconds. No grade braking is available in Range Selection Mode (Manual Shift Mode).

For grade braking to activate it requires the driver to apply steady brake pedal pressure to maintain desired speed while driving on a downhill grade. The vehicle’s modules monitor the amount of brake pedal apply, vehicle deceleration rates, and other factors to determine if normal mode powertrain grade braking is necessary. When the feature activates for the first time that ignition cycle, the DIC will display “Grade Braking On” or “Grade Braking Active” and you will notice the transmission downshifts and engine RPM increases. At this point, if the brake pedal is released the transmission will hold the current gear. If additional engine/transmission braking is needed to help maintain the desired speed, reapply steady brake pedal pressure and additional downshifts may occur.