DIM = driver information module (instrument cluster)
CEM = central electronic module (buss connector for all computers)

Testing a turbo? Vibration, but that cannot really be detected without taking off the intake air lines and checking the spindle for lateral movement.

When the DIM fails, the speedo can go to zero and the other gauges may fail, and the engine goes into limp home mode. Sometimes it will leave you stranded.

When the CEM fails, all sorts of strange error messages will appear, seemingly unrelated. You will get tranny and engine errors and possible shutdown.

I would skip ANY Volvo made in 2000 and 2001, as they are all error prone and costly to repair. Don't forget about the electronic throttle module fiasco of 1999.
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My back feels better when I sit in a Volvo seat