4WD Low Range Speed Control 2018 Silverado

Liberator13 · July 8, 2022

I'm running into a strange situation trying to control my downhill speed in 4WD Low Range in my 2018 Silverado 1500 Z71. The background is that I was coming down a secondary road mountain pass. So it was a few miles of gravel/rock 3-7 degree slope. Fairly wide open in parts, and blind corners in other parts. In older trucks, I would put the truck and 4lo and 2nd gear to keep the speed I want.

I tried to keep a steady speed on a 7 degree downhill slope 3 different ways.

1) Manually selecting 1st in 2hi. This did offer some engine braking, but once the speeds got to 20mph I would have to hit the brakes, because that was a little too much speed for the trail. This is the truck operating as I expect. The trail is just too steep for 2hi.

2) Putting the truck in 4lo, manually selecting first gear and starting to roll without touching the pedals. This would hold the truck at 2mph without issue indefinitely, but this was far to slow for the trail. My expectation is that I could put the truck in 2nd gear and give it some throttle or brake to modulate my speed. As soon as I touch the throttle in first gear the truck would start rolling downhill with little engine braking. The truck ran up to 4k rpm in first gear before I hit the brakes and realized this is not a reasonable way to do the trail. Doing the same thing with 2nd gear selected yielded the same results.

3) Using 4lo and hill decent control seemed to work fairly well. I couldn't tell if engine was doing any more braking than it was is scenario two, or if HDC was actuating the brakes that much more. Edit to add: HDC would shut off after a few minutes and the truck would flash a "Service Stabilitrac" error. The light would shut back off after a fuel minutes and I could use HDC again if I want. I'm guessing it was trying to protect the brakes.

Has anyone else noticed this strange behavior (compared to older trucks)? Has anyone figured out a way to hold 10-15mph on a 7 degree slope without riding the brakes?

Edited July 8, 2022 by Liberator13
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newdude · July 13, 2022

On 7/8/2022 at 1:36 PM, Liberator13 said:

Has anyone else noticed this strange behavior (compared to older trucks)? Has anyone figured out a way to hold 10-15mph on a 7 degree slope without riding the brakes?

Yea. Go slower. You are trying to hold too much speed, which is why the HDC is disabling. Its over working the ABS pump to hold the brakes. You would be better off modulating the speed with your foot on the brake pedal.

Liberator13 · July 13, 2022

42 minutes ago, newdude said:

Yea. Go slower. You are trying to hold too much speed, which is why the HDC is disabling. Its over working the ABS pump to hold the brakes. You would be better off modulating the speed with your foot on the brake pedal.

When I was actually using HDC, I was keeping my speed under 10mph. 15 would have been ideal for most of the trail. What's frustrating to me is that the truck offers next to no engine braking above 2mph in 4lo.