This could be a faulty turntable motor or a faulty control board.
If everything is working ok with the exception of the turntable then it would suggest the motor.
Call Bosch on 08444 810320 to have it repaired.
Bosch appliances have a 2 year warranty.
You are supposed to register the appliance but this is really just to get your name on their database for extended warranties.
Just give them a call, it could save you the cost of repair.
If they refuse, let me know and I'll advise further on tests and repair.
Hope this helps
Let me know how it goes or if you need more help