Get the fault codes read. That'll tell you why the engine management system is turning on the light. All you have to do is think through the possible causes.
Edit: Found this link (Which you should have found if YOU had done a search). It seems quite helpful, especially posts 11 and 12.
Unfortunately, I can't tell how relevant these suggestions are, as you have not told us the exact model/engine. This should give you enough to get a long way to having it sorted.
http://forums.digitalspy.co.uk/showthread.php?t=1984682
http://www.allcorsa.co.uk/forums/showthread.php/corsa-c-ecu-46506.html
http://www.ecutesting.com/catalogue/vauxhall_eculist.html?category=4046&model=450
https://www.bba-reman.com/
Anon, February 2017
