Transmission downshifts when braking on hills. Is this a feature that can be "turned off"?

[YoRuddy]

Hi all,

2004 330i zhp with auto transmission. 42k.

1) When I drive down a fairly steep hill (Not San Francisco) the transmission downshifts automatically when I apply the brakes even sparingly. This can happen when the car is cold or hot. The downshifts are pretty severe send the rpms up to 4500 - 5000. In order to prevent this I have to shift in to sport mode and manually shift the car. As you can imagine this get very annoying.
2) When I drive the car at the beginning of the day (Engine and Trans. are cold) the transmission does not engage right away when i put it in Drive (D). It can take five to ten seconds before it fully engages.

My mechanic has no feedback for me on the first item other than: "It is probably programmed that way to heat up the CATs; and drive it in sport mode"
He has no explanation for the second item citing that transmission services are not due yet and that I should not flush the trans. due to all the junk that gets released.

I bought this car in April 2012 with 2.5k on it. I do not race it around or mistreat it.

Can someone please help with this?

Thanks,
YoRuddy

[Johnmadd]

Sounds like sticky clutch packs in the transmission, although I have no experience with e46 automatic transmissions.

[az3579]

I believe it does that to aid in engine braking going down a hill. I do not think you can turn it off.

As far as changing the fluid goes, it doesn't have enough miles on it for there to be any significant amount of gunk built up. Personally, I would change the fluid, every 30k.

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[YoRuddy]

Thanks for the feedback.

[WOLFN8TR]

I believe it does that to aid in engine braking going down a hill. I do not think you can turn it off.

As far as changing the fluid goes, it doesn't have enough miles on it for there to be any significant amount of gunk built up. Personally, I would change the fluid, every 30k.

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X2...

My ZHP does the same thing while descending down a hill. If you tap the brakes real quick the trans will down shift. It was an option called:

Hill Descent Control (HDC).
For a smooth and easily controlled decent when negotiating steep downhill gradients of up to 15 percent. Hill Descent Control (HDC) allows drivers to concentrate fully on steering without having to brake.

[johnrando]

Yup, item #1 mine does the same thing.
Item #2, don't know. To flush or not to flush is the million dollar question on auto trans... BMW says NO, many people say yes, do it.

[Hermes]

You have low enough miles, if you can afford it I think you should do two transmission flushes. One soon, and another in 500-1000 miles. Honestly, with the autobox it probably takes 8 or more to fully change out the fluid because some old stuff is always trapped.

The other thing you need to know is that the transmission fluid MUST be changed in the air. You dump and fill until slight overflow, then start the car and put it through the gears, leave it in D and fill the rest of the the way until it overflows again. It's a PITA but helps the shifting smoothness a lot when you change out the fluid.

I also changed the filter on mine
http://img.tapatalk.com/d/13/09/18/5uva8aqu.jpg

[danewilson77]

X2...

My ZHP does the same thing while descending down a hill. If you tap the brakes real quick the trans will down shift. It was an option called:

Hill Descent Control (HDC).
For a smooth and easily controlled decent when negotiating steep downhill gradients of up to 15 percent. Hill Descent Control (HDC) allows drivers to concentrate fully on steering without having to brake.

I thought that was the feature that slowed you on Hills while employing cruise control?

What's that one called then?

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[az3579]

Hill Descent Control only comes on X-Drive equipped cars. It is a feature that will apply the brakes for you when going down hills so you don't lose control while going down a snowy road, for example. IMO it is useless because it doesn't let the car go faster than walking pace.

The autos downshifting is just the way it's programmed and is not the same thing as Hill Descent Control (HDC).


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[danewilson77]

Hill Descent Control only comes on X-Drive equipped cars. It is a feature that will apply the brakes for you when going down hills so you don't lose control while going down a snowy road, for example. IMO it is useless because it doesn't let the car go faster than walking pace.

The autos downshifting is just the way it's programmed and is not the same thing as Hill Descent Control (HDC).


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So what is the feature called that slows a car in cruise control while going down a hill?

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[az3579]

The only system that would do that doesn't only apply to hills. It's called adaptive cruise control and works regardless of whether you're on a hill or not. Mainly designed for highway use, it still works at speeds as low as 30.

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[YoRuddy]

Thanks all for the feedback. I believe that the downshifting is probably a programming issue. I did get a DME update soon after buying the car but the problem has persisted. Since the Tx fluid is ten years old despite the low miles, I think that I will at least get a service before the scheduled interval and see how that works out.
Cheers

[az3579]

It downshifting isn't going to change with a fluid service. Maybe a transmission software flash, but that probably won't make it behave the way you want to since it's supposed to do that. Try aftermarket software instead of OEM.

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[Hermes]

Agreed, but fluid change will help keep his transmission shifting smoothly which he will notice. The downshifting issue might be able to be adjusted with transmission software upgrade, maybe eurocharged can do something about that

[JKO_ZHP]

Don't know how to get rid of it but I can tell you that it doesn't hurt the car. I live on top a hill at a very steep incline so I travel up and down on a daily basis - I thought it was unusual that it did this when the 325Ci didn't but it's been 35,000 miles later, and it still downshifts but nothing is showing signs of wear. (Currently at 106,000 miles)

[Dave1027]

You have low enough miles, if you can afford it I think you should do two transmission flushes. One soon, and another in 500-1000 miles. Honestly, with the autobox it probably takes 8 or more to fully change out the fluid because some old stuff is always trapped.

The other thing you need to know is that the transmission fluid MUST be changed in the air. You dump and fill until slight overflow, then start the car and put it through the gears, leave it in D and fill the rest of the the way until it overflows again. It's a PITA but helps the shifting smoothness a lot when you change out the fluid.

I also changed the filter on mine

Agreed except you don't top off in D. Go through the gears, warm up the tranny to 100 degrees f and top off in P.

[Cabrio330]

Comforting - in an odd way - to read that someone else is experiencing the same problem as I have had for a couple of years now - see my previous thread on this exact issue:

http://www.zhpmafia.com/forums/showthread.php?5406-Odd-Steptronic-Downshift-Problem-Any-ideas

Dealer did a fluid flush and replace for me and if there was any improvement, I can't tell. I even emailed Mike Miller and he admitted he had never heard of this problem.

[Dave1027]

Actually, I like that feature. It shifts basically how I would shift it if it were a manual. I'd downshift if going down a hill and I wanted to slow down.

[LivesNearCostco]

Dane, I think it's called... Cruise Control! :pimp

Actually I was wondering... when you're doing that and the hill causes the car to go faster than the set speed, does cruise control just reduce throttle or does it actively apply brakes to keep the speed down? In my car I swear it feels like it's applying brakes if the hill is steep enough, but I can't tell for sure.


So what is the feature called that slows a car in cruise control while going down a hill?

[Cabrio330]

Dave1027, I don't think you would like what we are experiencing, unless you enjoy downshifting from 5th to 2nd and popping the clutch! It is nearly that drastic!

[danewilson77]

Dane, I think it's called... Cruise Control! :pimp

Actually I was wondering... when you're doing that and the hill causes the car to go faster than the set speed, does cruise control just reduce throttle or does it actively apply brakes to keep the speed down? In my car I swear it feels like it's applying brakes if the hill is steep enough, but I can't tell for sure.

Right. I thought that was called HDC, because all cars don't do this.

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[Hermes]

Agreed except you don't top off in D. Go through the gears, warm up the tranny to 100 degrees f and top off in P.

I've heard of it being done with both methods, my buddy uses the one in D his personal cars and has had no issues over the years

[az3579]

Right. I thought that was called HDC, because all cars don't do this.

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To quote my earlier post:


The only system that would do that doesn't only apply to hills. It's called adaptive cruise control and works regardless of whether you're on a hill or not. Mainly designed for highway use, it still works at speeds as low as 30.

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