Vectra 1.9 150bhp

My spanner light comes on everytime I start the car but only stays on until I've driven it for a few minutes then goes off and doesn't appear again, this is usually when I first start the car up or after not using it for a few hours. Doesn't cause me any problems as far as I know and it passed all the computer tests!

just the light is bugging me! I've just had it fully serviced aswel!

Any ideas why it keeps coming on? previous owner said something about the glows???