2004 Hyundai Sonata 2004 Sonata Won't Pass NYS Inspection -

I have a 2004 Hyundai Sonata 6cyl automatic that won't pass a New York State inspection because of emissions failure. The check engine light was on for a while a few months ago, but it turned off and I drove it for a couple thousand miles after that with no problems. I have tried to get it inspected a couple of times and it keeps failing because of the computer check for emissions. It seems to run great, and passes everything else except for the computer emissions check.

My dealership is going to charge me $100 just to get it in the door, so I am going to see if I can pinpoint the problem first and maybe fix it on my own. Has anyone experienced a problem like this before and have any ideas?

Thank you!