dim headlight lamp?

I have just had my citroen picasso motd and one of the failures was when the headlights are put onto main beam the lamp on the dashboard goes on like it is supposed to. When the headlights are put onto dipped beam the main beam light does not go out but just dims. Can anyone help please. The car is a Citroen Xsara picasso 2002 model 2.0 SX hdi