Parking Brake and Auto Stop

[CTown Duramax]

Strange Auto Stop Start Engagement


This is a 100% repeatable thing. 2021 Tahoe LT diesel base 4WD. (This is a wonderful SUV. No criticism here. Just getting used to the features. I have never liked a car as much as this one.) Has anyone else seen this and what do you suggest?

Start without disengaging auto start-stop. Back up out of garage turning up hill and stop with front facing down hill and and rear going up hill. Foot on brake. Shift to park. Engage parking brake. Foot off brake. Then remember to disengage auto stop-start.

The car lurches forward one or two inches onto the transmission park pin or maybe the parking brake reengages - that's how I would describe it, a small lurch forward onto another stop. Foot on brake. Engage drive. A sort of snapping noise as the car goes into drive. Release brake. So I do not know what the sound is, whether it is the parking brake letting go or the transmission coming out of park.

To have the car move on the parking brake is alarming. The noise is not gunshot loud, but one of those noises a machine shouldn't make.

Maybe there is some interaction among auto start stop, hill assist and the parking brake.

The grade is somewhat steep. I estimate 20%.

I forget the auto start stop half the time. Maybe I will get that module. I was hoping to avoid messing with a brand new car.

MY SOLUTION FOR NOW is not to turn off auto start stop when on a hill. The auto stop does not operate in this situation - i.e., the engine keeps running.

 

[Micahsd]

On my '21, I've just gotten into the habit of pushing the starter button, then after a second push the auto-stop button...yes, it's annoying to hit two buttons all the time, but I'm so used to it now, when I get into my wife's Traverse and start it up, I start looking for the auto-stop button.

When it comes to parking on a hill, what you describe is probably what would generally happen when placing it into the regular Park where it would lurch forward a little to have the transmission stop it. I don't typically put mine into park on a grade/hill, but when i do I'll usually engage the electronic parking brake which is a seperate button (which makes a weird mechanical noise around the rear wheel area). I believe that would be the proper procedure when parking on a steep hill and to not have it rely on the actual transmission Park, but maybe others can chime in on that.

 

[CTown Duramax]

Thanks for answering. I appreciate it.

Yes, I did engage the parking brake before letting my foot off the brake. It was then - foot off brake - that I saw auto stop start was still on and I disengaged it. After disengaging auto stop start, it seemed to me that the parking brake let go and the transmission pin in park took up the load. If I do not touch the auto start stop, it doesn't happen. If I disengage auto stop start just after starting - a habit I am trying to develop - this phenomenon does not happen.

The reason I am backing out and engaging the parking brake at all is to get the Tahoe (with kids in the back seat) out of the garage for my wife. Our tiny garage opens onto a short driveway and a narrow, steep alley - not ideal full-size SUV conditions.

I will have to go through all this again carefully. I'll set this situation up and take careful notice if I can disengage auto stop start with my foot still on the brake. It could be just like you say, simply that the parking brake slips a little on the hill and that there's a loudish noise when taking the parking brake off on an incline.

If that's the case, my electronic parking brake is not engaging as firmly as it should. Is there an adjustment for this?

When I say no criticism here, I really mean it. I am not a certified GM mechanic, far from it. (I have no idea how to work on this generation of cars.) I am not saying that there is any defective condition. All my comments are subjective. My concern would be avoiding undue wear or damage to the transmission.

I'll perfect my auto stop start habits!

 

[Micahsd]

I’d guess there’s some sort of test or adjustments they can make.

I think it does a self test every so many starts (usually it’s a brief loud noise coming from the back wheel when you shift it into park).