4WD Low - "Engine Braking"

[cbgrant74]

I noticed an interesting feature in my 2015 Silverado the other day. To descend a very steep hill on a logging road (20+ percent grade), I put the truck into 4WD low and M1. I eased over the crest, and the truck descended the hill at less than a walking pace with my foot off the brake. It held the RPM's around 500 unless I stepped on the gas to speed up. If I got the RPM's over about 1,000, it would "let go" and lose the "engine braking" effect until I slowed it back down with the brakes. When I reached the bottom of the hill, the truck nearly came to a stop.

 

The truck is not a Z71 and does not have Hill Descent Control (HDC). (It has the NHT max trailering package, so no Z71. Six-speed transmission, 5.3 engine, 3.73 rear end.) I can find nothing in the manual or elsewhere explaining this feature/behavior. As I understand HDC, it uses the brakes to maintain speed (similar to ABS or traction control), but there is no ABS noise or brake pedal pulsation when this is happening. HDC also sets a fixed speed, while my truck would slow down or speed up based on the steepness of the grade. It seems like this is more than just regular engine braking, as the engine maintains idle speed (500 rpm) even with the truck pushing it down the hill.

 

Has anyone else noticed or experienced something similar?

[newdude]

Sounds normal to me especially with you being in M1 and 4LO. That's a lot of engine and driveline braking right there.

[TxTruckMan]

That's just 4LO. Grade braking is not active when in M.

[Z45]

I agree, having owned a 4x4 since the 1970's, that's typical for 4x4 lo range. If you go over a certain RPM in 1 st gear the trans will up-shift automatically to the next gear. Its like that to prevent red-lining.

[kstruckcountry]

One of the many situations 4lo can come in handy.

 

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