The first step is to have the codes read by a diagnostic machine. There are many causes of this fault including wheel speed sensors, steering wheel angle sensor and of course the famous Continental ATE ABS/DSC Hydro unit failure - either the mechanical (pump) or electronic (module) elements of this unit.
In my case it was the DSC/ABS pump. I sent the whole unit to ECU Testing near Derby. They were great. Don't send it to BBA Reman - they were hopeless.
I'm not saying you have the same problem as me but my post may be of interest to you. One consolation for you is that the ABS/DSC unit for the 4 cylinder engines is less costly than for the 6 cylinder units - should a repair not be effective.
See
http://www.e90post.com/forums/showthread.php?t=813999
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