There have been quite a few threads about these subjects. It got me wondering about something.


In the owner's manual-

Powertrain Braking
For vehicles with a 6 speed automatic tranmission, when driving on steep descents where frequent
braking is required, the vehicle will automatically downshift to provide engine braking assistance.
This feature also reduces brake temperatures and wear.

Downshifting will only occur when the driver's foot is applied to the brake. Active Select Mode can
be switched on to override the feature and gain complete controll of shifts if desired.


Is it possible that this is occurring when the driver isn't pressing the brake? Because symptoms seem
to point towards it. At any rate, people with these kinds of problems should see it disappear if they
use Active Select Mode. If those drivers want to, is a different subject.


Has anyone looked into this and I just didn't see it after searching?

I'm wondering some more...

This is speculation, but we've seen already that the G8 has had a recall for the braking lights coming on.
I don't have knowledge of the root cause or of how the problem was fixed, however, could it be that there are
times when the car thinks it's braking when it's not? Did GM execute a recall to only make the lights go out without taking
care of the real underlying isuue? Sort of like putting a Band-AidŽ on a rash?

no, mind does it without my foot on the brake, and its not even on a steep incline, it will do it from 40-48mph going straight non incline coasting. DOD seems to keep it from doing it, but with my superchips tune i have DOD dissabled

no, mind does it without my foot on the brake, and its not even on a steep incline, it will do it from 40-48mph going straight non incline coasting. ...
ditto

I guess it's not clear how I put it. That's exactly when I'm saying. Is this Powertrain Braking happening
when people don't even have their feet on the brake? Has anyone seen 1/4 mile videos of G8s with the brake
lights on going down the track? Their feet aren't on the brake yet the lights were on. The recall took care
of the lights coming on. Is there an underlying issue in the braking system that the transmission is thinking that
braking is being commanded? These seperate topics and threads sounds like they could be releated.


Can anyone with the tools and/or tech knowledge of the G8 and it's systems confirm any of this?

Thoughts?

I've experienced this too and it really annoys me. Feels more like the torque converter remains locked when I let off the gas, rather than unlocking like it should to allow a steady coasting effect...

Mine too; not only on steep dwongrades, but 40-45mph while "coasting" wihtout braking. Weird

Is there an underlying issue in the braking system that the transmission is thinking that
braking is being commanded?

I think you're on to something.

If the brake light switch is misadjusted so that the brake lights stay on, then the transmission would think the brakes were applied. They must run off of the same switch. I can't believe GM would waste money and weight putting in two switches.

Mine does the weird engine-braking-while coasting thing sometimes. I'm taking it in next week for the brake light recall. (Even though the brake lights behaved properly when I tested them myself.) We'll see if that fixes the weirdness.

Mine too; not only on steep dwongrades, but 40-45mph while "coasting" wihtout braking. Weird

Same here... It ONLY happens between 40-45mph and its only on slight hills. It's fine on steep hills.

I took my car up Mt Washington last summer (used to be the true testing grounds for cars back in the early 1900's) and on the way down, I kept the car in first gear. No surging, it just held the car at 16mph. Once I got to a lesser grade, I shifted second, kept the car around high 20's, no surging.

Around town, slight grade, 40-45mph, it keeps triggering back and forth, and it DOES feel like the converter. It's probably between some value in a table for holding speed. Its weird and annoying.

... I'm taking it in next week for the brake light recall. (Even though the brake lights behaved properly when I tested them myself.) We'll see if that fixes the weirdness.
The brake recall didn't fix mine.

Brake recall didn't fix mine either. Also, is it a coincidence that the torque converter locks-up around 40 to 40mph and the coasting issue at the same speed? I really think the torque converter is confused so it is locking and unlocking back and forth and that's what we're feeling when coasting.

Mine didn't start doing it till after the recall work was done