Replacing the system fan - ThinkCentre M90 (type 3245, 3491), M90p (type 3269)
Attention Do not open your computer or attempt any repair before reading and understanding the "Important safety information" in the ThinkCentre Safety and Warranty Guide that came with your computer. To obtain a copy of the ThinkCentre Safety and Warranty Guide, go to the Lenovo Support Website.
This section provides instructions on how to replace the system fan. To replace the system fan, do the following:
Turn off the computer and disconnect all power cords from electrical outlets.