oiling the fan bearing may get you by but ultimately it needs to be replaced. There will be a part number on the fan label.  If you remove the label and the fan doesnt show the bearing its because there is a rubber cap over it. Take that off and then oil then put cap back. Wipe excess oil off because the label wont stick if its oily. Add a drop or 2 with the fan laying flat on the table. Then hold the fan and move the blades to work it in. 4 rubber grommets hold the case fan in. You will need to remove the fan. Putting it back requires pulling the rubber tabs back thru the holes with needle nose pliers. [URL]   System Fan Removal [IMAGE]     What size? [IMAGE]   [URL]   [URL] [IMAGE] [IMAGE]   [IMAGE] [IMAGE]      
Have an Optiplex 9020 (full size?) and have just started receiving the message "rear fan failed : F1 to continue ; F2 for setup, etc. The "rear fan" then runs mostly at full speed - obviously I would say the sensors st*&fed, as the fan is still working, just not controlled. If I disconnect from the motherboard, all seems ok (including temperatures...). 1/ anyone know what the problem is? Any way to fix sensors? OR2/ OK to run the PC without the rear fan... I realize the speed control can be disabled in the BIOS, but that just means everything runs at full speed. Thanks.
Optiplex 9020 rear fan fail