There are a whole lot of sensors and actuators on the engine. If any one of them fails or gives an out-of-range signal the engine management light comes on and a fault code is stored.
Depending on the model/year/engine code of your car you may be able to read the codes yourself, but it may be better to take it to a garage or diagnostics specialist to have the codes read.
Dont go to a Vauxhall dealer, they're too expensive, go to an independent garage. A basic code read should cost about £30, post a new thread with the results and we'll take it from there.
sigg
July 2009