Service light and check injection?

Hi. I have a 2005 Clio III 1.5dCi. As soon as I turn on the ignition, after the dash light check the service light comes on and a few seconds later the 'check injection' message on the display. Car starts fine and drives well. Fuel consumption could be better (I get 50mpg at best driving like my mum). There is a bit of a knock like over-fuelling and I get a fair amount of black on the tailgate and bumper like she's running 'a bit rich', although not smoky from the exhaust unless I accelerate hard. Also, though totally un-connected from this problem, the fuel gauge reads high by about a quarter tank and the indicated mpg and fuel usage are miles off.