Step son says its not working any ideas?

Did he change rim sizes?

Link for assistance
https://mbworld.org/forums/clk-class...e-control.html

No wheel changes. Just out of the blue no cruise control.

The cruise is linked into the same circuit that controls other items on the car, therefore if one is at fault it can cause the cruise to stop working:

Process of elimination:

Cruise only works from 30mph and above.

So the wheel sizes are good, is the tyre tread wear from front to back fairly consistent?

Is there any warning signs on the dash eg, ABS / ETS / EPS? If so than this could be due to a faulty break switch (Very Common) and will inturn shut down the cruise.

Is the ABS working? (jump on the brake in gravel to try)