If mechanical damage see below:

If mechanical damage (for example a destroyed compression wheel) is found on the turbocharger, just replacing the turbocharger is not enough. To avoid subsequent damage later, perform the following steps: 

• Check the air filter housing, air filter element and air duct hoses for contamination.
• Check the entire charge air circuit and charge air cooler for foreign objects.
• If there are foreign objects in the charge air system, clean the charge air circuit and replace the charge air cooler if necessary.
• If bearing damage is apparent on the removed turbocharger, change the engine oil and filter.