My engine management light is on, but my car seems to run fine?

Hello I'm 19 and I have a year 2000 Ford Focus 3 door hatchback, since Tuesday I have noticed my engine management light is on, on my dash. My car seems to start up okay and run okay and ticks over like it should. It has 1 little moment on Wednesday morning when I started it up and it shuddered before running smoothly again, it also did this when I revved it once that morning… But apart from that little moment on Wednesday, it seems to be running smoothly. I'm going to get it seen to at the garage on Tuesday but what is likely wrong? Light just needs reset? Or maybe something is wrong but isn't serious yet?

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