I used a simple Snap-On diagnostic computer that my buddy uses in his repair-shop, we used the OBD II interface to hook it up to the Benz. No need to decipher codes this way as the codes come up 'readable' on the screen along with the corresponding trouble code itself. The machine I used is fairly basic /low end Snap-On, I would think most auto-shops have one. As far as reading codes off of the car and deciphering them, I dont know of a link, but I'm willing to bet that there is one somewhere.
Hope that helps a little,