Sounds like a turbo overboost condition often caused by the variable vane ring in the turbo being stuck. Your turbo, a VNT type does not have a conventional wastegate. Instead the turbo boost is controlled at source by the ECU which alters the angle of the vanes to provide more or less boost to suit all engine requirements. If the vane ring becomes stuck due to the build up of carbon deposits and rust, and will not move then the turbo boost pressure can become too high. The ECU will detect this via the turbo boost pressure sensor and will take action by reducing the engine power before serious damage results. In this condition the fault code 17965 is often generated.

The cure is not necessarily a new turbo, although I expect the dealer will tell you it is. What it needs is to be removed and thoroughly cleaned. There is a product on the market which I have used with success. For less than £50 it's worth a try, but make sure you use it exactly as per the instructions.

http://www.innotecworld.com/products/sets-systems.php?productid=6