It works by controlling the torque and slippage to all four wheels from information that it gathers from various sensors. If it's not working properly then I would think you should be getting a warning and/or code unless maybe there is something wrong with a sensor that is reporting reasonable information that isn't accurate, like maybe the yaw sensor (not sure about what it's called.) Just spit ball' in though, mine works fine and I don't have any experience with DSC systems.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)