One of the problems with these is the 6 speed gearbox. very nice for economy but prevents the engine holding high revs for long on the motorway.

Last one I had I put two Forte Diesel treatments in it, cleared the codes and took it for a high speed (and revs run). Then advised the customer to use a lower gear from time to time to generate heat and bring the DPF into regen mode. (He does a 40 mile motorway commute)

The warning came on once breifly the following week and has been fine since.

HTH

Nick