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Hill Descent Control 2016 GMC Sierra

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Lines Of Code

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Question anyone? On a 2016 GMC Sierra 4x4 SLE 5.3 with cruise control but didn't come with Z71 offroad. Looking at the wiring diagrams shows Hill Descent Control is one wire from the body control module to the center stack switch assembly and once the switch is pushed applies a ground to that wire activating the system. If you were to install the correct center stack stab switch assy with the Hill Descent Control button, could it be that easy to acquire the complete system functionality?

JimCost2014 Senior Enthusiast

JimCost2014

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18 hours ago, Billy Sunt said:

On a 2016 GMC Sierra 4x4 SLE 5.3 with cruise control but didn't come with Z71 offroad.

I am not sure which one you are describing, since you brought up cruise control:

Hill Descent Control (HDC) If equipped, HDC can be used when driving downhill. It sets and maintains vehicle speed while descending a very steep incline in a forward or reverse gear. The HDC switch is on the center stack, below the climate controls. Press 5 to enable or disable HDC. Vehicle speed must be below 50 km/h (31 mph). The HDC light displays on the instrument cluster when enabled. HDC can maintain vehicle speeds between 3 and 22 km/h (2 and 14 mph) on an incline greater than or equal to a 10% grade. A blinking HDC light indicates the system is actively applying the brakes to maintain vehicle speed. When HDC is activated, the initial HDC speed is set to the current driving speed. It can be increased or decreased by pressing the +RES or SET- steering wheel controls or by applying the accelerator or brake pedal. This adjusted speed becomes the new set speed. HDC will remain enabled between 22 and 60 km/h (14 and 37 mph); however vehicle speed cannot be set or maintained in this range. It 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. 5 must be pressed again to re-enable HDC. When enabled, if the vehicle is at a speed above 22 km/h (14 mph) and less than 60 km/h (37 mph), a DIC message will display. See Vehicle Speed Messages 0 164.

 

Normal Mode Grade Braking If equipped with a gasoline engine and an automatic transmission, Normal Mode Grade Braking is enabled when the vehicle is started, but is not enabled in Range Selection Mode. It assists in maintaining desired vehicle speeds when driving on downhill grades by using the engine and transmission to slow the vehicle. The first time the system engages for each ignition key cycle, a DIC message will be displayed. See Transmission Messages 0 162. To disable or enable Normal Mode Grade Braking within the current ignition key cycle, press and hold the Tow/Haul button for five seconds. When the button is released, the requested mode change is made. A DIC message displays. See Transmission Messages 0 162. For other forms of grade braking, see Tow/Haul Mode 0 295 and Cruise Control 0 311. 

Lines Of Code Enthusiast

Lines Of Code

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After reading the owner's manual says when you first start the truck initiates a lamp test in the cluster and on my truck the HDC green light does not illuminate so I infer by that the HDC system is inactive and simply installing the switch won't make the system function. It would more than likely require the body control module to be programmed/flashed. Looking at how the HDC system works tells me 90-95%+ of the trucks equipped with it is never used since most trucks are driven on pavement only. If it was just installing the switch bank for $30 OK but not worth pursuing any further. Thanks for the replies.

JimCost2014 Senior Enthusiast

JimCost2014

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19 minutes ago, Billy Sunt said:

After reading the owner's manual says when you first start the truck initiates a lamp test in the cluster and on my truck the HDC green light does not illuminate so I infer by that the HDC system is inactive and simply installing the switch won't make the system function. It would more than likely require the body control module to be programmed/flashed. Looking at how the HDC system works tells me 90-95%+ of the trucks equipped with it is never used since most trucks are driven on pavement only. If it was just installing the switch bank for $30 OK but not worth pursuing any further. Thanks for the replies.

It does work, and for someone who has never used it, they would probably be a little alarmed on the noises and how the truck reacts when it is engaged.

 

Like the grade braking feature, it has to be in the "sweet" spot for it to kick in. Once engaged, the truck does slow itself down into a "rock crawl" mode. so a lot of things are going on.

 

If you off road a lot, maybe worth looking into, if you never go down a steep hill in the dirt/sand/snow, probably not worth it. Or even think to use it during the winter on a snowy/wet hill, just another feature never used in the Z71 package.

 

 

newdude Senior Enthusiast

newdude

Posted
Posted
22 hours ago, Billy Sunt said:

Question anyone? On a 2016 GMC Sierra 4x4 SLE 5.3 with cruise control but didn't come with Z71 offroad. Looking at the wiring diagrams shows Hill Descent Control is one wire from the body control module to the center stack switch assembly and once the switch is pushed applies a ground to that wire activating the system. If you were to install the correct center stack stab switch assy with the Hill Descent Control button, could it be that easy to acquire the complete system functionality?

 

 

It is not plug and play, nor can it be retrofitted.

 

 

Waffle34 Enthusiast

Waffle34

Posted
Posted
On 1/2/2021 at 11:04 PM, JimCost2014 said:

It does work, and for someone who has never used it, they would probably be a little alarmed on the noises and how the truck reacts when it is engaged.

 

Like the grade braking feature, it has to be in the "sweet" spot for it to kick in. Once engaged, the truck does slow itself down into a "rock crawl" mode. so a lot of things are going on.

 

If you off road a lot, maybe worth looking into, if you never go down a steep hill in the dirt/sand/snow, probably not worth it. Or even think to use it during the winter on a snowy/wet hill, just another feature never used in the Z71 package.

 

 

yea i have it in my z71 and hardly use it. Don't see the need honestly. I use it just to play with it and it is funky - think of activating the ABS constantly as you decent so its that growly grabby noise. If it slows too much it lets it roll then ABS kicks in again and can be kinda jerky. Id be afraid to use it in the winter honestly but I dont even like normal ABS on snow. (altho the system in these trucks isnt half bad - my 01 rangers , 02 blazers and 92 jimmy systems can go straight to hell though and i pull the ABS fuse every winter in them)

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JimCost2014 Senior Enthusiast

JimCost2014

Posted
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4 hours ago, Waffle34 said:

yea i have it in my z71 and hardly use it. Don't see the need honestly. I use it just to play with it and it is funky - think of activating the ABS constantly as you decent so its that growly grabby noise. If it slows too much it lets it roll then ABS kicks in again and can be kinda jerky. Id be afraid to use it in the winter honestly but I dont even like normal ABS on snow. (altho the system in these trucks isnt half bad - my 01 rangers , 02 blazers and 92 jimmy systems can go straight to hell though and i pull the ABS fuse every winter in them)

Lots of wet steep hills in the Seattle area during the winter months, that is when I try to remember to use it (and do once in a while).

Waffle34 Enthusiast

Waffle34

Posted
Posted
52 minutes ago, JimCost2014 said:

Lots of wet steep hills in the Seattle area during the winter months, that is when I try to remember to use it (and do once in a while).

Does it work well? We dont really have hills in IL haha. Most we get is rolling slopes or they salt the piss outa the few steeper roads.

  • 2 years later...
Lines Of Code Enthusiast

Lines Of Code

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On 1/2/2021 at 9:50 PM, newdude said:

 

 

It is not plug and play, nor can it be retrofitted.

 

 

Revisiting this issue again and noticed your reply. I can see that HDC wouldn't simply be plug and play by just installing the correct Stability Control Switch bank with the HDC added. The HDC switch simply supplies a ground to the body control module in the wiring diagrams and my truck has cruise control required for HDC to function through the + and - buttons. If the correct body control module was installed or reflashing the currently installed factory one? If you could explain "nor can it be retrofitted" would be appreciated.

newdude Senior Enthusiast

newdude

Posted
Posted
13 hours ago, Lines Of Code said:

Revisiting this issue again and noticed your reply. I can see that HDC wouldn't simply be plug and play by just installing the correct Stability Control Switch bank with the HDC added. The HDC switch simply supplies a ground to the body control module in the wiring diagrams and my truck has cruise control required for HDC to function through the + and - buttons. If the correct body control module was installed or reflashing the currently installed factory one? If you could explain "nor can it be retrofitted" would be appreciated.

 

 

GM won't allow flashing of the BCM to add that option.  They don't offer an approved path or provision to add it, therefore they don't allow it. 

 

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