Why you need diagnostic mode?
Suggest to find service manual first?
Toshiba have several service modes (input check, output check, test print, adjustment, setting mode, etc.)
Each of them have different entry.
It is not recommended to clear the PM counter manually.
A lot of problems will be arised if you do so.
Since the PM message will not affect your copier, use it as usual.
After it is locked up, replace a new Process Unit and the message will be gone automatically.
Kenny 
Linear Mode
