Think this relates to your dpf filter in your exhaust,do you do a lot of town driving/short journeys? It really needs regenerated and someone with the correct computer will be able to do this for you or try giving it a good run at very high revs at a constant speed and it should regenerate itself,that will depend how badly blocked the filter is,it is advisable to change your engine oil also but the computer should be able to tell you how badly the oil is degenerated with constant regenerations,any doubt replace,good luck
cdc, December 2015
