Your '04 has 40K and is considered high mileage? Mine has almost 80K. So far, the only code that comes up is for a lose gas cap.
Thankfully for me I have absolutely no intention of ever taking my XF to the one and only Chrysler dealership in the area. Their service department is awful; what cost you $400 would most likely run past $1000 for me since there still is the mindset here that women know nothing about cars.
I know there are lots of people on this site that either work in the service departments or have had great experiences with them; too bad none live near me.