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Discussion Starter #1
Hey guys

So I was headed down a two lane highway tonight when a rescue squad car flew up behind me, lights siren and all. I was doing about 60 and had a car next to me on the right while going up a hill. I popped it over into sport mode and tried to kick it down a gear to get the heck out of the way but somehow in the rush of it all managed to pop it down two gears. Suddenly I'm at 60 pinging the rev limiter in 2nd at 7k. Car is still running and acting normal, but my question is: I thought the ECM prevented manual downshifts into a gear that could redline the engine? From what I can tell the car was in 5th to get power up the hill, switching to sport mode dropped it to 4th, and I was attempting to get 3rd (from experience if you need a lot of power at 55-60mph 3rd is what you want) and ended up with 2nd. All I can say is downshift happens. Hopefully no damage in the long haul.

Thanks
 

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2009 CTS 3.6 LY7
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285 Posts
I would imagine it should be designed to disallow a potentially damaging downshift. But it's not something I want to experiment with.
 

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Black Tesla Model 3, long range, AWD
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689 Posts
I know the gearbox will downshift itself if you lower your speed in a high gear and don't change the gear yourself but outside of that I think the gear changes are up to you. Though I've noticed that when driving in manumatic mode the car doesn't allow me to upshift to a higher gear (say 5th gear from 4th) if my speed isn't high enough.
 

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'14 CTS-V LongRoof; '16 ATS-V Sedan,' 04 Trailblazer 4x4; '10 CTS LongRoof gone but never forgotten
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14,145 Posts
No harm no foul. I have done this, too. Keep on keeping on.
 

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2013 Black Diamond CTS4 Premium Coupe (sold-09 CTS4 DI Black Raven/Ebony)
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I would imagine it should be designed to disallow a potentially damaging downshift. But it's not something I want to experiment with.
That's why used car dealers have CTS's on the lot...so you can test out this theory. :highfive:
 

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Discussion Starter #6
I was thinking that because the car doesn't allow you to upshift beyond a certain gear at low speeds, it wouldn't let you downshift beyond a gear at high speeds.
 

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2008 SRX V8AWD- 2012 CTS AWD Wagon-'17 CT6 3.0TT
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Hey guys

So I was headed down a two lane highway tonight when a rescue squad car flew up behind me, lights siren and all. I was doing about 60 and had a car next to me on the right while going up a hill. I popped it over into sport mode and tried to kick it down a gear to get the heck out of the way but somehow in the rush of it all managed to pop it down two gears. Suddenly I'm at 60 pinging the rev limiter in 2nd at 7k. Car is still running and acting normal, but my question is: I thought the ECM prevented manual downshifts into a gear that could redline the engine? From what I can tell the car was in 5th to get power up the hill, switching to sport mode dropped it to 4th, and I was attempting to get 3rd (from experience if you need a lot of power at 55-60mph 3rd is what you want) and ended up with 2nd. All I can say is downshift happens. Hopefully no damage in the long haul.

Thanks
If you look down between your crotch you will see a pedal called the brake. If would have been wise to use it as the approaching squad would have also seen your brake lights and informing them of your upcoming evasive maneuver.
Also I think you were on a 4 lane hiway, unless you were passing going uphill? ;-)
 

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Discussion Starter #8 (Edited)
Technically a 4 lane highway, yes. My mistake. Hitting the brake wouldn't have been the best idea. By the time I saw him and began to make my move I couldn't see His headlights he was so close to me. I live in a very hilly area and didn't see him until he crested the hill behind the one I maneuvered on, which put him about 3 car lengths behind me and accelerating hard. If I had hit the brake I'm certain he would have rear ended me.
 

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2001 SLS & 2012 CTS
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My take would be... you bought a car with an automatic transmission. It will downshift "automatically" if you floor the throttle to accelerate. If it doesn't want do it automatically, then you probably shouldn't either. Don't overthink things.
 

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08 CTS DI AWD Luxury-Performance II ThunderGray/Titanium
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My take would be... you bought a car with an automatic transmission. It will downshift "automatically" if you floor the throttle to accelerate. If it doesn't want do it automatically, then you probably shouldn't either. Don't overthink things.
what he said!
 

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2012 CTS, thunder grey chromaflair
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Technically a 4 lane highway, yes. My mistake. Hitting the brake wouldn't have been the best idea. By the time I saw him and began to make my move I couldn't see His headlights he was so close to me. I live in a very hilly area and didn't see him until he crested the hill behind the one I maneuvered on, which put him about 3 car lengths behind me and accelerating hard. If I had hit the brake I'm certain he would have rear ended me.
This is taken from the owner's manual: "The transmission will only allow you to shift into gears appropriate for the vehicle speed and engine revolutions per minute (RPM). The transmission will not automatically shift to the next lower gear if the engine rpm is too high, nor to the next higher gear when the maximum engine rpm is reached."
 

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2012 CTS4 (AWD)
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118 Posts
I really don't think the 'manual' transmission in our CTSs is designed to shift on the fly in case of emergency. It's just not responsive enough especially on the downshifts as it tends to rev match the engine before shifting over, nullifying the braking effect of the downshift.

It's useful though, to maintain the car in the "correct" gear while maneuvering through a corner and still keeping the engine revs at the right power curve to allow power on exit.

On most automatic cars (not exotic supercars... duh...) this is what happens:

You approach a corner and stab your brakes then ease up on them to enter the corner and eventually release the pedal altogether, but the transmission tends to hunt for the highest gear possible so when you then eventually engage in the corner and you try and maintain your speed you're unable to because you have no power as the car is now in 4th, 5th or sometimes even 6th. You try using the throttle to maintain your speed in the corner and then be on the power on exit but you waste a half second or more while the transmission figures everything out and eventually "kicks down" as you give throttle on exit, by then it's too late and you've been passed on re-acceleration by your adversaries or worse, you over compensate by giving too much throttle and as the car downshifts into the correct gear it gives a jolt that might throw you off course or into a spin.

The correct way to use our manual mode is:

When you approach a corner you stab the brake and at the same time, find the gear that will give you the optimal power response from the engine (usually 2nd or 3rd gear depending on the cornering speed, you want to be ~3500RPM, not too high otherwise you'll have to up-shift right as you exit) and as you release the brake you can control the car by feathering the throttle.

Then on exit you can give full power and go up the gears or move back to automatic.
 
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