ive had this problem and it is manufacturers code, i was losing power on motorways when trying overtake wich brought on the engine light and a loss of power. 1st, remove egr valve and clean it 2nd in the inlet manifold underneath the egr valve there is a row of butterfly valves , clean these thoroughly and 3rd check the vac pipes to make sure there are no holes in any of these. hope this cures it .
dave hall
April 2010