Hill Descent Seems to Only Work Intermittently

MrLeadFoot · August 22, 2025

Like the title says, it seems to not engage all the time, although the indicator indeed illuminates on the dash. I've tried while going downhill with and without my boat in tow, on flat roads, and while going anywhere from 5- 25 mph. Tried pressing the button to turn it on while moving and from a stop. Sometimes engages, sometimes doesn't. Tried while rolling downhill without foot on the brake, and then again while braking. Same thing. Then, on Wednesday, while towing my boat it suddenly engaged when I was showing a passenger how it doesn't work, then later on the same drive it didn't engage again. Tried it in Normal mode and in Tow mode, in D and L transmission modes. User manual doesn't really say anything about any special conditions that need to be met to have the function engage. Is there a secret to this, or is mine malfunctioning? If it is malfunctioning, would this throw a code that a standard, non-Tech II OBDC reader would pick up?

Thanks in advance.

Edited August 22, 2025 by MrLeadFoot

newdude · August 23, 2025

Sounds like its not seeing enough of a grade via the yaw sensor data. Try leaving the off road page open on your DIC and see what the grade % is at on those roads you are trying to make it activate on.

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

MrLeadFoot · August 23, 2025

Thanks, Newdude, for setting me straight. I don't know how I missed that part about the grade percentage. That must be it. I remember using HDC on long boat ramps last year when the lakes were low, and it was nice, and it always worked, but I bet boat ramps are steeper than 10%.

This year I've been frequenting a lake that has some pretty steep grades going around its dam to the launch ramps. Instead of pumping the brakes, I remembered I have HDC, and when I tried it on the last 2 trips it only worked sometimes on the same grade. I bet it's because that grade is just about 10%. I have HUD so I will set it to the appropriate display to monitor the grade.

Again, thank you so much for pointing this out.

asilverblazer · August 25, 2025

Has anyone experienced a maximum distance or time it can be engaged?

In my previous truck (2015 GMC 1500 5.3, 6 speed with hill decent) it would turn off after an amount of time or distance with no warning. While going down a long steep rocky road/trail it would shut itself off which was rather unsettling when the truck would suddenly take off. I recall only a few other owner reports of this happening, but no determination if it was normal or a fault.

Haven't had any chance in my current truck to see if this remains.