As long as your C230 is a 97 or 98, you can read all the values. Press and hold REST for about 5 seconds to it up (AUTO & RECIRC (?) for Up/Dn/scrolling through codes.
Stored codes in the A/C system are retrieved a different way though.
Any more Questions? Please ask! Good luck.
2006 E350 w/ 155k miles (Daily Driver)
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)