Hiya Mate, The engine management light normally comes on when the ECU chip finds a fault with the car. Could be anything as it monitors quite a lot of info! the chip is essentially the cars brain and stores info about the faults. If you either A. Take it to a garage and ask them to read the chip, last time cost me £25, or another solution is to buy a fault reader and run the diagnostics yourself, you can buy the kit for the vauxhall for £18.99 at Halfords. We have just bought the tool to do it and its really easy, just unplug the ECU from its socket, plug the reader on to it, turn it on and it makes the engine management light flash a number of times. You count the flashes and double check them against the table of codes given and it directs you to whats causing the light to come on. Usually the fault will stay in the ECU memory until it is reset, so faults from the past can sometimes be tracked.
Best of luck in anycase
Michelle
Michelle, January 2005
