: Deceleration on Downhill



Cad96k
07-20-10, 10:46 AM
I'm a new Cadillac owner, so also new to this forum.

I've noticed something peculiar with my new 2010 SRX. When I go over a hill and begin the descent the car actually decelerates when I take my foot off the gas. With every other car I've owned, gravity will cause the car to accelerate.

In the morning I like to coast down my street while the car warms up but I can no longer do this as the car actually seems to be fighting gravity.

I called my dealer about this and he said he had noticed this.

If I slip the transmission into neutral, the car starts to accelerate as I expected it should.

Has anyone else experienced this, and is it normal?

TheCaptain
07-20-10, 12:25 PM
It is normal, the trans just kicks some extra drag on so you don't severely exceed the speed limit, and so you don't have to burn so much on the brakes when you get to the bottom (if need be).

Jake2010
07-20-10, 12:31 PM
Congrats on your new caddy and welcome to the forum! Your going to love the SRX, it'a a great car!

When I first got my SRX I thought the same thing, that the car was decelerating not just downhill but all the time whenever I took my foot of the gas. I know the engines today are built so tight that they naturally want to stop spinning when not under acceleration. I have 1500 miles on my SRX and noticed it's definetely better.

Just my thoughts on the matter! Enjoy your SRX!

TheCaptain
07-20-10, 12:33 PM
Oh ya, welcome and congrats on the purchase! Post some pics up in the new deliveries thread!

algiorda
07-20-10, 01:02 PM
Have you tried this in sport mode?

The transmission may be in a gear causing you to do engine braking. You may want to use the sport mode to change to a higher gear suggesting to the transmission to coast instead of brake. I'm sure it will adapt to this habit over time.

Cad96k
07-20-10, 01:15 PM
Thanks for the feedback. I'm glad to know it isn't just me! I did try Sports mode and even in 6th I can't get it to coast/accelerate with gravity. It will only coast in neutral.

I contacted Cadillac customer service and my dealer and both are investigating for me. It sounds like nobody has ever raised this as a concern because they couldn't cite any similar cases.

I would like to see an on/off feature, like they have for the traction control, to prevent the computer from trying to slow me down.

Gotta use gravity to my advantage with gas at today's prices!

ewill3rd
07-21-10, 09:10 AM
It all has to do with how the transmission is constructed and controlled.
As stated above it has to do with "engine braking".
When you lift off the gas the engine slows. If the transmission components are not designed to "overrun" or "coast" then the engine speed reduction will be translated into vehicle slowing regardless of what you are doing.
In most of our 4 speed transmissions there is no engine braking in overdrive.
Strangely more people complain about that then the situation you are in.

Without knowing the specifics I'd say this is a normal condition.
I don't know that they engineered it that way but...
Do you have the 3.0 or the 2.8?
The 2.8 has an Aisin transmission and it is built by the Japanese.
The 3.0 has a 6T70/75 which is a new transmission for us Cadillac guys but Saturn and some other brands have been using it for a while.

cz9h3d
07-21-10, 09:44 AM
The SRX with the 6T70 (3.0L V6) has automatic grade braking. I think pretty much all applications using this transmission employ this. Its intent is to eliminate braking excessively during a hill decent. You can't turn it off, and I believe the advantages (reduced brake pad wear, limited unwanted acceleration - and tickets) far outweigh the 0.0001mpg improvement you'd get without.

It doesn't bother me on mine.

PJ1520
07-21-10, 12:46 PM
Some vehicles I have had in the past, when set on cruise, would actually downshift on the downgrades to hold the set speed. I have not experienced that in my previous GM cars.

But now that you mention it, I don't recall having to brake on the downgrades on a recent 3,000 mile trip. Now you have me curious.

iamq
07-21-10, 01:07 PM
I'm with Cad96K on this one. This is the first thing I noticed when I got my SRX home. Here in New England there are lots of coasting hills. My other Gm car with 3.8 and 4spd auto coasts down hills, the engine rpm's drop to below a 1000 and speed picks up. If you shift out of OD it will engine brake. That car gets close to 30mph consistently. The Caddy engine brake keeps the engine between 1200 and 2000 all the way down thru the gears. With all the options with this tranny you'd think you could get this feature.

Cad96k
07-21-10, 10:58 PM
So, I went to my dealership today and drove a salesman's SRX with a few thousand miles on it. He has the same SRX engine as mine - 3.0, not the 2.8. He said he had noticed exactly what I was talking about but that it seemed to go away over time. Sure enough, I drove his to a couple of downhills and it did accelerate most of the time, although not every time. There was still some of this engine drag as mentioned by cz9h3z and the tech in this thread - thanks ewill3rd for that explanation, Customer Service didn't know what I was talking about when I contacted them and that was the kind of answer I was looking for.

My mission was to find out if this was normal so I wouldn't have to worry, and I guess it is. Just seems counter-intuitive to fight gravity. I can understand if the car is smart enough to maintain speed on a downhill so you don't have to use the brakes, but I don't think it should be engineered to actually decelerate; I thought that's what sports mode and downshifting was for.

:thumbsup:Thanks to everyone for weighing in. This is just something I'll have to get used to. Good to know I wasn't imagining it and that something wasn't wrong with the transmission or engine.

ewill3rd
07-21-10, 11:20 PM
When you lift the pedal the ECM really cuts back on fuel and the engine essentially becomes an air compressor.
It is kind of like a jake brake on a big rig if you know what that is, although not for the same purpose.

I never pay attention to it, but it is good to know.

I really pick up a lot of hints from you guys that I use when cars come in for service.
I am not aware of all the issues that can pop up but being exposed to this community allows me to be aware of things before I even have to work on them.
Makes my boss think I am even smarter too :lol:

davdat
07-22-10, 06:49 AM
My 2010 SRX 3.0 does the same thing, I have 1400 miles on mine. It's normal is what I was told by my dealer.

stevec5375
07-22-10, 08:28 AM
When you lift the pedal the ECM really cuts back on fuel and the engine essentially becomes an air compressor.
It is kind of like a jake brake on a big rig if you know what that is, although not for the same purpose.

I never pay attention to it, but it is good to know.

I really pick up a lot of hints from you guys that I use when cars come in for service.
I am not aware of all the issues that can pop up but being exposed to this community allows me to be aware of things before I even have to work on them.
Makes my boss think I am even smarter too :lol:

You are to be commended for this stellar attitude toward your job. I wish the same were true of the technicians at my dealership. When I mention the wealth of information on this forum, they just look at me like deer in the headlights. DUH.

iamq
07-22-10, 02:42 PM
Heres another situation where the engine brake is a pain. Today I took the SRX to the city, there is one street with lots of traffic lights. I used to be able to get the car up to 30 and coast to the next light. Not with the SRX, you have to drive on the throttle all the way... As soon as you get off the throttle the engine brake kicks in and you start going too slow.. uck...

leewillis1113
02-18-11, 12:37 AM
I own a 2005 cts and for a long time now whenever i go down a hill it will drop back into second gear and wont go back out til i put it in neutral and then back in drive and its fine but it wont otherwise, putting it in sport mode doesnt help either. I have taken to a cadillac dealer and they just take my money, and it still isnt fixed, anybody else have the same problem or know what could be wrong, i believe its some kind of sensor but I really have no idea, thanks for any input. Its the 6 cyl auto

Smokin' SRX
02-21-11, 11:53 PM
You do not have a 6 speed tranny, Right? We have a different animal. From your description, I think you have a true tranny malfunction. Get a free diagnostic at a tranny shop. Sorry.



Re: the 2010+ SRX, the above posts are spot on. In addition, I read in Road/Track or Car & Driver a while back, about a developmental problem with the 6+ speed trannys causing them to bog down alot, after a coast and then an attempt to accelerate (especially in turns) because they remained in a high gear. The solution was to downshift a bit (usually 1 gear speed I recall they said) so as to better accept the gas upon throttle up.

I know if you coast, modern engines are designed to turn off all fuel to the injectors, while coasting in DRIVE. Not so in Neutral. Nature of the beast.

SS

zinner
03-01-11, 05:50 PM
Something us manual transmission guys have been doing for a long time, engine braking. My wife also noticed it. It's even more prevalent in the 2.8T in sport mode. I used to do it in my Gen1 SRX by using manual mode on long descents specifically in the mountains. Keeps you from overheating the brakes.

It's definitely something new from GM.

PJ1520
03-03-11, 11:40 AM
With all of the Federal pressures on the manufacturers to increase fuel economy, and all of the practical pressure from customers looking for the same, this concept of introducing engine braking that is not driver-controlled makes little sense to me. I have had vehicles in the past that, while on cruise, would downshift automatically to hold speeds at the set limit on the downgrades.

PJ

Smokin' SRX
03-03-11, 01:08 PM
If they did not program it this way, you'd be in 6th gear ,coasting, coming out of a turn at 35 mph, and suffer an abrupt downshift to 3rd gear on throttle up. So it kinda keeps you in a more advantageous gear . But yup, kills coasting as we once knew it. And I would not recco you put into neutral while driving. To easy to loose control in an emergency. (even illegal in some states!)
JIMHO

SS