2004 Jeep Liberty Emission Code on Diagonostic

I have a 2004 Jeep Liberty in which the check engine light just came on. I took it to a local auto store and they hooked it to their diagonostic machine in which it spit out an emission code, but the young kid said it could be anything. Any idea what it could be? I'm on a tight budget and don't have tons of money to waste at an auto body shop?

Thanks!