# Automatic Differential Brake (ADB) + DSC



## jason929 (Mar 16, 2004)

I'm doing my research into the purchase of a new car. I'm looking at the BMW 330xi. All wheel drive is a must for my choice.

I was interested in how BMWs DSC system works exactly. Here's how I understand it: the DSC system is composed of several individual systems, one of which is the ADB. and via its use of ADB, the 330xi gains the benefits of a hypothetical limited slip differential on both the front and rear axels.

*question*: if I choose to deactivate DSC, a yellow light comes on in the control panel to indicate such. But this yellow light only indicates that DSC is no longer using engine power to control the car. In other words, ADB (selective braking on each individual wheel ) is still operating. Now if I hold down the DSC button for like 5 seconds, then it lights up a solid red and this indicates that ALL DSC functions (except ABS brakes) are turned off--i.e., the ADB system among others is now no longer functioning. Is this correct?

*Last question*: I've read some comments online from a guy who has a driveway with an uphill steep that when it is snow covered he can NOT drive up it without turning off the DSC. What I was unable to determine was whether he meant turning off the DSC entirely (i.e., red light) or just partially (i.e, yellow light). Would having the ADB operational hurt one's ability to ascend a snow covered driveway? It shouldn't right? it just operates like limited slip differentials--it should help it.

Any comments/corrections I would greatly appreciate. Thx all


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## dlloyd1975 (Sep 8, 2002)

jason929 said:


> I'm doing my research into the purchase of a new car. I'm looking at the BMW 330xi. All wheel drive is a must for my choice.
> 
> I was interested in how BMWs DSC system works exactly. Here's how I understand it: the DSC system is composed of several individual systems, one of which is the ADB. and via its use of ADB, the 330xi gains the benefits of a hypothetical limited slip differential on both the front and rear axels.
> 
> ...


I believe that the 'yellow light' is what he was talking about for steep hills. It specifically mentions in the owners manual that sometimes it is necessary to turn of DSC when negotiating such situations.

I believe that if you just click the DSC button once, DSC is stil active, but the limits are much higher. This may be a different situation on the xi's since the brakes are used to redirect torque in the AWD system. Holding it down does turn off everything but ABS. Again, this may be very different on the xi's due to the AWD system.

I believe that there was a pretty detailed discussion a while back if you search through the archives. Unfortunately, IIRC, it was pretty inconclusive.


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## jason929 (Mar 16, 2004)

dlloyd1975 said:


> I believe that there was a pretty detailed discussion a while back if you search through the archives. Unfortunately, IIRC, it was pretty inconclusive.


I tried doing a search but the engine isn't working.


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## RKT BMR (Sep 7, 2002)

dlloyd1975 said:


> I believe that if you just click the DSC button once, DSC is stil active, but the limits are much higher. This may be a different situation on the xi's since the brakes are used to redirect torque in the AWD system. Holding it down does turn off everything but ABS. Again, this may be very different on the xi's due to the AWD system.


Not quite right. Partial disabling of DSC (the yellow indicator mode) completely disables several of the DSC functions (traction control, torque control), while leaving some others (ADB) enabled.

Torque control is simply moderation of the engine throttle. This is an effective strategy to improving traction when there is significant traction at one of the rear wheels. ADB will keep the other wheel, with little traction, from spinning, causing the differential to transfer power to the wheel with traction. However, under those circumstances it is easy to break the traction wheel loose, so the system overrides your throttle inputs and moderates engine power when it detects a loss of traction on the one good wheel.

This, of course, is disasterous if neither wheel has good traction.. Basically, you won't be able to get anything spinning at the back end with DSC on. In some low traction circumstances, like a packed-snow covered road surface, some wheel spin is instead an effective means of *gaining* traction, so DSC gets in the way. However, ADB may still be very helpful.


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## Nick325xiT 5spd (Dec 24, 2001)

The guy who couldn't get up his driveway is Dougdogs. And he didn't turn off ADB because he CAN'T. He and I have both discovered that DSC does a nice job of stalling the engine in slippery conditions. If it's snowing, the first thing I do before I start driving is kill DSC. It's more dangerous to leave it on than off. (Assuming you know what countersteering and throttle modulation are.)


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## fkafka (Mar 12, 2002)

jason929 said:


> I'm doing my research into the purchase of a new car. I'm looking at the BMW 330xi. All wheel drive is a must for my choice.
> 
> *question*: Is this correct?
> 
> ...


1) On an xi, you get DSC-X, and you only get *one* level of DSC-X deactivation. BMW has been purposfully vauge about what this does, but consensus is that is dissables yaw control entirely, and diables traction control partially.

2) When the wheels start to spin, traction control shuts down wheel spin by applying the brakes. If traction control is set to be very sensitive on a a slippery slope, then you can't move forward at all because TC shuts your power down too quickly. Making TC less sensitive allows you to go forward.


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