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Thread: Is there any rear fan for Optiplex 745 SFF?

  1. #1
    Join Date
    Jan 2012

    Is there any rear fan for Optiplex 745 SFF?

    Hello there! I have Dell optiplex 745 SFF (form factor) and at the back of the motherboard there is something that looks like a fan plug. It is a desktop model. I get this BIOS error:
    • Alert! Rear Fan Failure
    • Alert! Air temperature sensor not detected

    By looking at this error, i suspect the my BIOS is searching for a fan with temperature sensor but there is no place to fit a fan in the desktop computer. Is there really any fan in the case except the one at front? Have you guys found any other fan inside your 745 SFF?

  2. #2
    Join Date
    May 2011

    re: Is there any rear fan for Optiplex 745 SFF?

    Yes, i have the optiplex 745 SFF and there is a fan under the hard drive. There is also a temperature sensor located on the front fan. There are 4 types of the chassis and here are the locations for the temperature sensor:
    • In mini tower: sensor is attach to signal cable
    • For desktop: integrated with front panel and shared with input output ribbon cable
    • Small form factor: sensor is located at front grill of the case in front of the fan 2.
    • Ultra small form factor: it is integrated into motherboard only so there is no wiring for that.

  3. #3
    Join Date
    Jul 2011

    re: Is there any rear fan for Optiplex 745 SFF?

    The boot error about temperature sensor is shown when cable from control panel connecting to the motherboard is disconnected. This message is to show that system did not detect or failed to detect the sensor. You will need to set the cable properly and then reboot your system again and see if it again shows that error message. If your sensor’s temperature is more than 42 C then system will show the error message in error log. Your system fan will make more noise if such condition is detected.

  4. #4
    Join Date
    Jan 2012

    re: Is there any rear fan for Optiplex 745 SFF?

    I have optiplex 745 SFF with Intel core to duo e4400 2 GHZ. When i start my system i get the popup like ”Alert rear fan failure. Press F1 ti continue and F2 to run setup.” Please help me solving this. This looks different than the error that other users are getting!

  5. #5
    Join Date
    Aug 2011

    re: Is there any rear fan for Optiplex 745 SFF?

    If your fan is not connected properly then make sure you have setup like this:
    1. connect the hard drive fan’s wire to the motherboard
    2. Connect the power and data cable to the drive

    • If you want to replace the rear fan then follow this:

    1. You will need screwdriver and BIOS update CD.
    2. Remove the computer cover by removing the latches
    3. Now remove the hard drive , below it there is the small fan located.
    4. Lift the release tab present on the back side of the fan panel
    5. On the back panel there is a arrow mark shown to fit the fan, you have to rotate it in opposite side.
    6. Once the fan is free lift it by using the screwdriver to remove it and its panel from hard drive bracket.

  6. #6
    Join Date
    Aug 2011

    re: Is there any rear fan for Optiplex 745 SFF?

    The error is mostly shown when dual core processor is used with 745 SFF with no disk fan. Dell BIOS seems to be searching the drive fan even if it is not present there in the system. The thing that worked for me was using the “sense wire”. I have yellow colored wire in my system and it can vary from computer to computer. It is near 5 pin connector. I connected that sense wire to front fan connector and then to the matching pin of the fan connector of the drive fan. After doing this setup rear fan was detected by the BIOS. You will need to buy old dell 5 pin fan to get the 5 pin connector. You can buy it from e-bay.

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