3.0 Diesels have Variable Turbo Geometry!Both wastegated and VTG Turbos are activated with Vacuum pipes.........................The difference being that if a pipe is loose on a wastegate,the turbo will overboost as no vacuum(air) reaches the valve for it to move the rod that opens the plate on the Turbo´s exhaust outlet to release pressure and thus controlling the boost.On a VTG Turbo, a loose pipe coming from a sensor would prevent the Geometry(vanes) from opening as the rod activated by vacuum would not move and would not receive adequate air from the turbo inlet pipe,which in this case the turbo would underboost considerably and as soon as you step on the throttle the car will enter SAFE mode.The same can obviously be said if it is overboosting!...

The VTG rod is also sometimes prone to getting stuck and spraying something like WD40 oil on it,will bring it back to life!