Question

I have a 2009 Dodge Avenger 4 Cyl. with check engine light on the code that comes up is 2004

Answer 1

check for intake leaks near the intake manifold 

the 2007-2008 had issues with the whole intake manifold, if your is a mid to late 2008 production it could have the same issue (mid to late 2008 production is considered 2009 model)

https://www.autocodes.com/p2004_dodge.html