Congratulations on your newly acquired C220. As mentioned, you have the OBD-II system for emmisions related diagnostics. This was mandataed by US federal law for all cars sold in the US from '96 up.
This is good news (in my opinion). You can read most of the engine and transmission related codes yourself for very little money.
The OBD-II electrical interface is located beneath the dash on the driver's side. All you need is a scanner to read this data.
Most dedicated scanners are expensive.. fortunately, in this case, there's a better way.
Try this link:
I bought this interface box from this guy and it works great. His site is pretty self explanatory. You download the software from the site, plug one end of the interface into your car and the other into your laptop... and bingo, you're in. It works great on my '96 S500.
One advantage it has over simple "scanners" is that it allows you to see the data as a "stream" and will plot the O2 sensor and fuel trim in real time. This is really helpful if you're chasing a "lazy" sensor that takes a long time to come on line.
Anyway, I'm sure others have good solutions and they will post here, but I use this simple (and inexpensive) OBDII interface on all my cars (both foreign and domestic) and it works terrific.
This will not let you access Mercedes specific code digital data for non-engine/transmission systems. You do need a specific (and expensive) scanner for that.
Good luck, hope this helps, KenP