2021 Yukon Denali - Sudden, Unexpected Slowdown from 67 to 50mph

[tagexpcom]

Was doing some winter camping/towing this week.... 2wd driving down a high-quality, 65mph, dry, 2 lane road on Adaptive Cruise at 67mph. Nothing in front of me but oncoming traffic/rows of 18-wheelers and cars whizzing by in the opposite direction when...

Suddenly, a sharp slowdown occurred, like stepping on the brakes suddenly/firmly. No skidding, but strong enough to pitch me forward a little in my seat. Significantly sharper than one would normally apply the brakes. I was just mouthing to myself 'what's going on' when it stopped - so just a few seconds. Slowed from 67mph to maybe 50mph before it let go. No alerts on the computer or screens that I noticed - was watching the heads-up display at the time. Didn't re-occur the rest of the 500 mile trip.

This is seriously concerning to me, especially towing and don't want a repeat! So I'd like to understand what may have happened.

Could this be adaptive cruise control mis-reading vehicles whizzing by in opposite direction? My experience so far with adaptive is a gradual slowdown - nothing like this.

Maybe I or they got close to the centerline? can this cause any kind of un-commanded slowdown?

Any other ideas?

Got my used 2021 last August, so still pretty new to Yukon Denali world, and thanks in advance for any thoughts on this.

(Not sure of the category so picked General Discussion)

 

[Pro299]

I expect that was your collision avoidance system having a hiccup. Mine did that often enough that I finally turned it off. I was afraid the sudden slowdowns would eventually cause an accident.

 

[tagexpcom]

I expect that was your collision avoidance system having a hiccup. Mine did that often enough that I finally turned it off. I was afraid the sudden slowdowns would eventually cause an accident.

How does one turn it off? I've been thru the onboard options menus and turned everything off (I think) that I could.

 

[tagexpcom]

Looking at my user manual, I see that ACC can apply braking automatically....


and FCA can also apply "mild" brakes.....


Just turned FCA off in Vehicle Personalization options - and everything else while I'm at it. Hopefully that will make things better. This automatic stuff is not good enough for real life. For example, the car/pedestrian warning has come on inappropriately several times so far. The latest was simply turning a sharp corner with a pedestrian on the sidewalk - car didn't take into account the turn.

And now, this uncalled for auto-brake incident is not good for me at least.

I don't like adaptive cruise control - doesn't work well, slows way too soon. The problem is the non-adaptive doesn't show on the heads-up. Another booboo.

Anyway, hope turning the FCA off does it!

 

[KMeloney]

If you don't like the ACC slowing "too soon," then maybe you can just reset the gapping parameters to something much shorter.

 

[tagexpcom]

Just took the rig out and because I turned things off, I'm getting a series of 'FCA is off', 'Y is off', messages on start. Annoying...

 

[StephenPT]

Just took the rig out and because I turned things off, I'm getting a series of 'FCA is off', 'Y is off', messages on start. Annoying...

They want it to be annoying - they want you to know every time you turn on your rig that it's turned off. The legal implications are too large these days for them not to give you a tell-tale...

 

[tagexpcom]

They want it to be annoying - they want you to know every time you turn on your rig that it's turned off. The legal implications are too large these days for them not to give you a tell-tale...

Agreed, but then they should do a better job and not make it my problem. Un-commanded, unexpected, *unwarranted*, strong slowdown from 67mph. This was not a gradual take you're foot off the gas slowdown. Strong enough that someone could rear-end me for example. A warning or flashing symbol is way different than interfering directly with my driving control.

A feature that works 99% of the time is not good enough (in my opinion) when it has side-affects that can be dangerous. This is not a self driving or partial self driving rig, it's 100% human driving required and a *strong* (scary) slowdown loss of control, taking away the acceleration option from the driver, could also hinder rather than help avoid a collision.

Not picking on Yukon or GMC - speaking in general with all the new vehicles I presume. My last new one was 2011 - pre this kind of stuff.

Cannot imagine what's happening with self-driving rigs / taking hands off the wheel when you just feel that this stuff is only 99.9% and not 110%

 

[clogan2]

My '16 has "lane keep assist" (LKA) that auto corrects steering if you start to stray out of your lane. I was driving around Birmingham, in left outside lane of 6-lane I-459, with a semi to my right. The semi drifted into my lane. I reacted by quickly veering to my left. The LKA sensed my leaving my lane, and "auto-corrected" by steering me back against the semi. Very nearly a disaster. I now keep LKA turned off.

 

[Boatguy]

My ‘17 Denali will do exactly that when on ACC and I’m overtaking another vehicle and the road is a slight left hand turn. The ACC mistakes the vehicle (usually a truck) in the other lane as being in my lane and hits the brakes pretty darn hard. I’m to the point that I see that situation coming and turn off ACC before it happens.