2003 Other Ford Models Engine Management Light

Engine Mechanical problem
2003 Other Ford Models Manual

Hi, I have a Ford KA the engine management light is on. The car itself runs fine, never had any problems with it, even now when the light is on. Although when the car is stationary and the clutch is put down there is a a knocking sound, once it is gear the noise goes and the same when it is in neutral. I know I need to have a diagnostics test done, but was just wondering if you have any sort of idea what could be causing this.

Thanks

Trudi