Volvo C30 2008
 

I have recently bought a Diesel C30 (2008), which i have to say is in excellent condition, but was in need of a service.
I've done a full service, Oil change and filter, air filter, (cabin filter (that was fun !!) and coolant flush which went swimmingly. Undercabin all wax oiled. I then changed the fuel filter, which was problematic when trying to prime, however got there in the end.
The problem is that I am now getting "Engine System Service required" message, that will not clear and it would appear that the Turbo is not engaging as the car is now very sluggish. ODBC error when connected is P0238 - Turbocharger Boost Sensor A Circuit high.
Any suggestions on where to look would be appreciated.