I read the post below about how to access the "hidden' radio features to see the radio's serial number, etc. and how to change the auto-volume stuff where it increases the volume at speed. Kris L said it only worked on the business CD, but I want to clear that up. I have the Business Cassette headunit, and no Harman Kardon upgrade, and it worked fine on my headunit. I thought it was pretty cool. The feature where you press the preset buttons and it tells you how strong the frequency is or whatever from 1-15 is really cool. It was very informative. I like finding out these little things about my car.