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2015 Acadia SLT AWD
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Discussion Starter #1
The scenario of my 2015 3.6L AWD SLT-1:
I live near the Rockies and so do a certain amount of mountain driving.
Often, I will leave the shifter in manual Low and do the shifting myself while in the mountains at normal
highway speeds and have no problems.
However there are times when I have the tranny in D and come around a corner and then into a steepish
downhill (5%) grade. So, I back off the gas and pull the shifter back into manual L. For whatever reason,
the transmission computer ALWAYS selects 4th gear....instead of 5th gear. I've tried all sorts of ways to get the tranny
to select 5th in this situation but no joy. The tranny computer (PCM ?) MUST be programmed to select 4th gear no matter
what. Yes, I understand the logic behind this is that if you do shift into manual Low under these conditions, you must want
to slow down really quickly and thus the programming is set up to select 4th instead of 5th......but this is awfully hard on the drivetrain IMO.
Bottom line, I like to think I know how to use a manual transmission after racking up hundreds of thousand of miles driving
motorcycles and trucks with manual trannys......as opposed to how GM's computer programmers BELIEVE the tranny
SHOULD be shifted..
Is there anyone out there who is intimately familiar with the tranny control computer programming who would know how to make
such a change in the program ?? To my untutored mind, it would seem to be fairly easy to change the program in this one respect.
Has anyone out there had experience with hooking up a laptop and/or a diagnostic tool and making such a change to the PCM
program ??
Yes, I know this is a petty thing....but's it's REALLY annoying to a guy used to manual transmissions.
Any help and/or comments are greatly appreciated.
 

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I've used 'L' many times while driving in mountains, or other times when I wanted to manually shift. I've never seen it as a real problem to tap the + button and put the trans into 5th. You'll likely have to find a 'tuner' to reprogram the transmission to downshift into 5th instead of 4th when 'L' is selected at highway speed. It's doubtful anyone at a GM dealership will do it for you.
 

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The scenario of my 2015 3.6L AWD SLT-1:
I live near the Rockies and so do a certain amount of mountain driving.
Often, I will leave the shifter in manual Low and do the shifting myself while in the mountains at normal
highway speeds and have no problems.
However there are times when I have the tranny in D and come around a corner and then into a steepish
downhill (5%) grade. So, I back off the gas and pull the shifter back into manual L. For whatever reason,
the transmission computer ALWAYS selects 4th gear....instead of 5th gear. I've tried all sorts of ways to get the tranny
to select 5th in this situation but no joy. The tranny computer (PCM ?) MUST be programmed to select 4th gear no matter
what. Yes, I understand the logic behind this is that if you do shift into manual Low under these conditions, you must want
to slow down really quickly and thus the programming is set up to select 4th instead of 5th......but this is awfully hard on the drivetrain IMO.
Bottom line, I like to think I know how to use a manual transmission after racking up hundreds of thousand of miles driving
motorcycles and trucks with manual trannys......as opposed to how GM's computer programmers BELIEVE the tranny
SHOULD be shifted..
Is there anyone out there who is intimately familiar with the tranny control computer programming who would know how to make
such a change in the program ?? To my untutored mind, it would seem to be fairly easy to change the program in this one respect.
Has anyone out there had experience with hooking up a laptop and/or a diagnostic tool and making such a change to the PCM
program ??
Yes, I know this is a petty thing....but's it's REALLY annoying to a guy used to manual transmissions.
Any help and/or comments are greatly appreciated.
The programming is complicated and what one might believe to be a simple change can have a negative impact on other elements of the drivetrain.

As another that has driven manual transmissions since the 60's, You really can't compare driving a manual trans to a modern computer controlled automatic.
 

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The transmission is default programmed to downshift into the lowest "safe" gear vs. whatever RPM band you're in at the current driving condition. So yes, at 60+ MPH it will pop into 4th, maybe rarely 3rd.

However, try the same thing at 30 MPH and it will often times put you into 3rd, maybe even 2nd depending on what the computer is interpreting.

There is no way to overcome this without custom aftermarket programming. It's actually a really annoying quirk. Even my wife's Buick Encore will just put the transmission into shiftable mode while maintaining the current driving gear without downshifting.
 

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isnt it doing what older cars did?
If you were in D, and shifted to 3 it shifted down 1. (are you in overdrive, then it would technically shift down 2)?
In my Traverse-
If im in D and going down the highway at say 60-70 (and in overdrive)... and I need to pass or something similar, I simply shift to L, knowing that its going to drop me to 4, and get the engine RPMs up, simultaneously pressing the gas, the engine/trans/vehicle responds well to the increase in RPMs and the gas input. I then simply shift to 5, then 6- once I'm out of the situation.
 

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2015 Acadia SLT AWD
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Discussion Starter #6
isnt it doing what older cars did?
If you were in D, and shifted to 3 it shifted down 1. (are you in overdrive, then it would technically shift down 2)?
In my Traverse-
If im in D and going down the highway at say 60-70 (and in overdrive)... and I need to pass or something similar, I simply shift to L, knowing that its going to drop me to 4, and get the engine RPMs up, simultaneously pressing the gas, the engine/trans/vehicle responds well to the increase in RPMs and the gas input. I then simply shift to 5, then 6- once I'm out of the situation.
In my 2015, I cannot select gears with the +/- button when in D. Being able to select gears with the +/- button when in D would be the ultimate solution, of course, but GM seems to think that their owners/drivers are not mentally capable of making such "complex" decisions.....and for 90% of Acadia drivers, they're probably correct. I just happen to be in the 10% that
like, in some situations, to do their own shifting.
 

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Discussion Starter #7
isnt it doing what older cars did?
If you were in D, and shifted to 3 it shifted down 1. (are you in overdrive, then it would technically shift down 2)?
In my Traverse-
If im in D and going down the highway at say 60-70 (and in overdrive)... and I need to pass or something similar, I simply shift to L, knowing that its going to drop me to 4, and get the engine RPMs up, simultaneously pressing the gas, the engine/trans/vehicle responds well to the increase in RPMs and the gas input. I then simply shift to 5, then 6- once I'm out of the situation.
Older cars, yes, but you could manually shift the old 4 speeds just as you replied....one gear at a time. In my Acadia from D, I would prefer to have it drop down to the next lower gear (5th) when I select L at highway speeds and NOT 4th gear.
My other option is to select L from startup/driving away then shift manually the whole time. I have done this occasionally when the terrain dictates doing so and it works great.
I'm just not big on computers/GM programmers making ALL my decisions for me, especially gear selection.
 

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...
My other option is to select L from startup/driving away then shift manually the whole time. I have done this occasionally when the terrain dictates doing so and it works great. ...
That's not true. Select 'L' and press '+' to the highest gear desired before starting out. The transmission will shift as it should until that gear is reached.
 

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In my 2015, I cannot select gears with the +/- button when in D. Being able to select gears with the +/- button when in D would be the ultimate solution, of course, but GM seems to think that their owners/drivers are not mentally capable of making such "complex" decisions.....and for 90% of Acadia drivers, they're probably correct. I just happen to be in the 10% that
like, in some situations, to do their own shifting.
When that mood strikes me, I just hop in the Corvette. :)

You seem to be faulting GM for accommodating the vast majority of their owners. I've never had the urge to manually shift my Acadia. Don't even know if manual mode even works.
 

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Discussion Starter #12
That's not true. Select 'L' and press '+' to the highest gear desired before starting out. The transmission will shift as it should until that gear is reached.
You're right. I should have been more descriptive in my post. It will work either way though.....pre-select or shift manually all the way through
 

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You'd like the paddle shifters in the XT5. The transmission can be downshifted one gear at a time while the the gear selector is in 'D' just by tapping the '-' paddle. The display shows 'D(gear).' If the '+' is tapped while cruising, it will display 'D' along with the current gear. The 'D(current gear)' display reverts back to just 'D' in a few seconds. I haven't worked with the downshifting function enough to find out if the downshift cancels itself and the transmission shifts back into the original gear. Stay tuned!
 

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Discussion Starter #14
You'd like the paddle shifters in the XT5. The transmission can be downshifted one gear at a time while the the gear selector is in 'D' just by tapping the '-' paddle. The display shows 'D(gear).' If the '+' is tapped while cruising, it will display 'D' along with the current gear. The 'D(current gear)' display reverts back to just 'D' in a few seconds. I haven't worked with the downshifting function enough to find out if the downshift cancels itself and the transmission shifts back into the original gear. Stay tuned!
Yes, that sounds EXACTLY what I want/need.....but the Cadillac price is out of my ,league. LOLOL
Thanks for the info, though.
 

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Yes, that sounds EXACTLY what I want/need....
Maybe you should read the owners manual for your next vehicle before you purchase it.
 

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Discussion Starter #16
Maybe you should read the owners manual for your next vehicle before you purchase it.
I'll take that remark as a kind suggestion.......however.......
sadly the owner's manual for my 2015 is rather.....let's say opaque.....about the actual details of how the PCM makes its "decisions"
as to what gear it selects in various situations. This is something I've noticed in my last 2 GM vehicles. It seems that GM doesn't
want to burden its owners too much "technical" information when it comes to the powertrain. One interesting factoid about the
powertrain is that the manual states that the tranny fluid should NOT have to be changed for the lifetime of the vehicle......
and we all know that such a statement is not really applicable to real-world driving.
There is actually faaaaaaar more info on the passenger restraint, entertainment and HVAC systems than there is on the tranny
and AWD systems.....so the owner's manual would have been of very limited help with regard to my original question.
As well, this vehicle was bought used and the salesman was only fully cognizant of the then-new model features available,
which happened to be the 2017 models. I'm not sure if the new gen Acadias have a different shift program or not but it's a moot point now.
 

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Newer owners manuals are a bit more transparent. Here's a brief description of Manual Mode for the 2018 Acadia: "If the transmission is in 6 (Sixth) gear when L (Manual Mode) is selected, a downshift to 4 (Fourth) will be commanded. If in 5 (Fifth) through 2 (Second) a single downshift will occur."
 

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Discussion Starter #18 (Edited by Moderator)
Newer owners manuals are a bit more transparent. Here's a brief description of Manual Mode for the 2018 Acadia: "If the transmission is in 6 (Sixth) gear when L (Manual Mode) is selected, a downshift to 4 (Fourth) will be commanded. If in 5 (Fifth) through 2 (Second) a single downshift will occur."
Thank you for that info.
Well, it's nice to see they've cleared that up in the new gen owner's manual.
However, I'm going to see if there is any way that someone with a genuine GM scan/programming setup could make the change I want.
 

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Thank you for that info.
Well, it's nice to see they've cleared that up in the new gen owner's manual.
However, I'm going to see if there is any way that someone with a genuine GM scan/programming setup could make the change I want.
Not worth it. Just drive in 'L' when you want full(ish) control.
 

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As previously stated. just quickly hit the + button when you go to L and it will go right to 5th, there's a decent pause after you shift so this just isn't that difficult a thing to do or warrant custom programming IMHO...
 
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