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Auto Grade Brake

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9 hours ago, shadow gray 2020 hd said:

Ok.  I know the exhaust brake has a switch/button, but thought you were talking about the button on the right side of the row of buttons that has the symbol of the truck going down hill.  Have never used that button.  


fwiw, my truck does seem to downshift going downhill after pushing the brakes to come off cruise.  But has not been in any way aggressive.  I will pay closer attention.  

Hello again my friend! Yes that button you are talking about is the "Hill decent control" button, I believe that only works under speeds of 25-30mph. Thank you for your feedback though I really appreciate your time and please keep me updated!

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Yupp, that button with the truck going down a steep hill under a speedo dial is for HDC.

I've had several trucks equipped with it, but so far haven't used it.


Hill Descent Control (HDC) 


(HDC) sets and maintains vehicle speed while driving down steep grades in a forward or reverse gear.
The HDC switch is on the center stack, below the climate controls.


Press HDC switch to enable or disable HDC.

Vehicle speed must be below 50 km/h (31 mph).


When enabled, the HDC light displays on the instrument cluster.


A blinking HDC light indicates the system is actively applying the brakes to maintain vehicle speed.


HDC can maintain vehicle speeds between 1 and 22 km/h (1 and 14 mph) on grades greater than or equal to 10%. 


If HDC is to be used for more than three minutes or on grades steeper than 25%, the transfer case should be put into Four-Wheel Drive Low (4 L) to reduce the possibility of brake overheating.


Noise from the Electronic Brake Control Module (EBCM) is normal when HDC is active.


When HDC is activated, the initial HDC speed is set to the current driving speed. It can be increased or decreased by pressing +RES or SET- on the steering wheel, or by applying the accelerator or brake pedal.

This adjusted speed becomes the new set speed.
HDC will remain enabled between 30 and 60 km/h (19 and 37 mph); however, vehicle speed cannot be set or maintained in this range. HDC
will automatically disable if the vehicle speed is above 80 km/h (50 mph) or above 60 km/h (37 mph) for at least 30 seconds.
Switch must be pressed again to re-enable HDC.

HDC may disable after an extended period of use.
If this happens, HDC will require time to cool down. The length of
time HDC remains active depends on road conditions, grade, set speed, vehicle loading, and outside temperature.


When enabled, if the vehicle speed is above 30 km/h (19 mph) and below 60 km/h (37 mph), a DIC message will display.

Edited by redwngr
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I have a June 2019 build date. There is a hill by my office that is 35mph, the truck has always kept me from running away when going down it. I have not been to the office much since March or so but went in the last two days and could not get the truck to maintain speed any of the three times I went down it. last service that updated any software was in the March time frame. 


Edit to add it was a Service Update Bulletin (N192285430): Engine Control Module Calibration Error

Edited by sdelam
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  • 1 month later...

Replied to this thread in the problems thread but i think it's been deleted. Had the computer update for the DEF sensors, now exhaust brake works even less; only works when in tow/haul mode. Took in today for service. They had no updates, even called GM technical service line. Looks like not enough of us have reported. 

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