Perhaps you fine gents can help me with this..

I've noticed a really strange thing with my astra (2000 1.6 SXI) and can't work out what the hell is happening:

Whenever I do a ton or over for a period of say more than a few seconds.. my engine management light comes on. It then stays on until I switch the engine off and back on again. Is my car trying to tell me something? I don't redline it through the gears to get to this speed it's a steady (most of the time unoticeable) climb from 70ish in 5th gear.

Can anyone shed some light?

Ooh, and before the AOC constabulary have a pop; I've had the car since september last year and this has only happened twice which indicates how often I do these speeds in my car (not very).

Spanks muchly..