steady/flashing check engine light on my S500

[Jim O'Keefe]

I was driving home from wallyworld a few minutes ago when the check engine light went on. I stopped, looked under the hood....nothing amiss. Shut off the engine, disconnected the battery, reconnected the battery, started the engine.....now the light is on continuously.......drove slowly home.....light goes back to flashing after a couple of miles.......I can't find anything that tells me what it means/why it would change......help please