This message came up after I had accelerated hard and suddenly lost power as the car went into safe mode,as most of you thought , this is going to be expensive.
Wrong ,forget all the sensors bearings , solenoids etc . The solution is simple ,

The main air intake pipe from the air box to the turbo is collapsing at one or both ends as you floor the accelerator .this is because the turbo sucks all of the air out of the pipe rapidly and atmospheric pressure compresses the pipe cutting off the air supply .

Hence Turbo Underboost......

The solution ....Cut to size a piece of 3inch and a piece of 2inch diameter plastic drain pipe
(Sizes may vary from car to car ) and insert into the ends of the air pipe fix in place with a screw clip or good cable tie ,reattach to car and rev away to your hearts content.
Hope this helps, keep in touch

Regards amalgam21