2003 Chevy Trailblazer service engine soon light?

Same happened to me. It would come on, then a few days later it would go off. Took it to Jiffy Lube for an oil change, and they came in and told me that the connector to the light was loose. So they pluged it back in. And its fine now. I believe Auto Zone does a free diagnostic test. You could do that to see if anything is wrong first. Hope that helps