Dash board engine management icon?

The electronic icon on the instrument cluster of my 2000 Vauxhall Astra 2l diesel keeps coming on every 63 seconds but is immediately extinguished when I apply the brakes. These symptoms apply both mobile and stationary. The vehicle has done over 100,000 miles and other than a starting problem if unused for more than a day (almost cured by a diesel additive) I am delighted with the car.