Your engine light usually comes on when an engine sensor is not relaying the correct signal to the ecu. Its could be any of the sensors malfunctioning. The best way to find out is to analyse the fault code from the ecu... You can either go to a vauxhall dealer and they cound tell you or do it at home. Here is a link to a guide.
http://www.topbuzz.co.uk/info/fault_codes/fault_codes.htm
Hope this helps you.
Ben Citrine
January 2008