service engine soon

I own and drive a 1995 Cutless Ciera Oldsmobile. My “service engine soon” light is coming on: it stays on, constant and has been doing it for about two weeks now (this has never happened before) - what are the possibilities of what the problem might be?
Thank you – Diane
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Your gonna have to go get the codes read at an Auto zone or O'Reilly. I would do it asap

Your gonna have to go get the codes read at an Auto zone or O'Reilly. I would do it asap

Thank you for your help on this