The supercharger clutch may not be working, but it doesn't necessarily mean
that the clutch is defective. There are certain other problems where one of
the many sensors can produce a signal to the ECU where the ECU will then
feel that things are out of whack enough that it is not a good idea for the
supercharger to run, so it disables the supercharger from kicking in. If
your mechanic is basing his diagnostics on a code alone, I would be
sceptical. If he has tested the clutch manually, then I would have more
confidence in his diagnosis.
If you read the various w202 forums and SLK 230 forums, you will see
numerous posts where mechanics misdiagnose supercharger issues as being
problems with the supercharger when the problem was realy elsewhere.
Numerous unecessary supercharger replacements. Dealers are not immune from
this mistake either. Bad sensors, undiagnosed vacuum leaks, etc., have been
posted as the real root cause of the problems after further investigation.