See if any codes are stored in the unit.

1. Turn car on.
2. Set climate control to LO
3. Press and hold Rest and Defrost simultaneously until a new menu appears (about 5 seconds), should read DIA.
4. Using the auto button (not sure which one on your car) you can scroll through the diff numbered codes. Write the codes down and report them back here.

I just learned of this little trick the other day. It worked on my 1995 C280... but I tried it this evening on a 1999 E430 and could not get it to work. Give it a try and see what you come up with though.

I'll check the CLK and see if I can get it working on that.
Good luck!

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
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!)