I have had this issue for some time now and it has been annoying me immensely. Mine had about 102000 on the clock when it first went on the dash and I wondered what it meant. A garage wanted 65 quid just to check it and then if there was a problem, extra cost to fix, so I had to leave it. It was intermittent, but then, recently, it came on and stayed on. Since moving, I have found a mobile mechanic I can trust and he told me there is a system in the exhaust [in the middle somewhere] that works this, so I asked him how much to replace with a new one. When he mentioned a figure bigger than the value of my 2007 car, I thought 'trade it fast,' but then read somewhere about how the injectors, when grubby, can make this go off, so I tried some Carlube type 'Redex.' It has only been a few days but within about ten miles the light went off and it has stayed off, with all symptoms vanishing and all because I bought some additive for the diesel last week. I am hoping I have fixed it and will be using the stuff again. Best £6-99 I ever spent. Got to be worth a try eh? Better than £65 plus costs that may not even fix it.Just thought I would share.