My Fabia engine light comes on & off on dashboard for no apparent reason. My mechanic cannot find any problems. Why is this happening?

Anyone know? Does it indicate an underlying problem?

Lady driver.

It;s quite possibly one of the sensors failing. A proper diagnostic scan will tell you, but unfortunately they aren't cheap. You might have some luck if you see whether there is a member local to you with the kit to do it, for the cost of a few beer tokens, though. Depending on the model of the car, I would guess it is either the coolant temperature sensor, the MAP sensor, or the MAF sensor. All of these 'die' slowly, so some days you might have a problem, and others you might not.

Hope this helps, and welcome, by the way!