CPU Fan Not Detected

By jonathanreuter2
Mar 20, 2007
  1. 2 Questions: My CPU fan recently stopped working. I had it replaced but the repair shop told me I would not be able to do anything about the error message on startup of, "CPU FAN NOT DETECTED" and that I would have to press F1 each time on startup in order to continue. Is there any way to remove this message?

    Also, how do I create a default OS so that I do not have to choose from the list of 2 at each startup? These two issues are quickly becoming an annoying start to booting up my computer.

    Thank you.
  2. chamillitarysk8

    chamillitarysk8 TS Booster Posts: 128

    go into control panel>system>advanced>startup & recovery then u can chose default and disable 2nd one from coming up
  3. jonathanreuter2

    jonathanreuter2 TS Rookie Topic Starter

    the OS problem is fixed. thanks chamillitary. If anyone else could help with the fan issue, I would be grateful. Thanks.
  4. captaincranky

    captaincranky TechSpot Addict Posts: 11,700   +1,886

    It must be working hard, Listen to all the noise

    Did the repair service install a 4 wire or 3 wire fan? Many boards have PWM fan monitoring which requires a 4 wire fan. Is the fan speed still being controlled by the mobo? I find it intriguing that the shop knew it wouldn't work correctly before you took it home.
  5. jonathanreuter2

    jonathanreuter2 TS Rookie Topic Starter

    It was replaced with the same exact fan from another Dell Dimension 2300, however, the message won't stop but I don't know why. I also figured that he should have known how to stop it, since i'm being charged money by this "professional". I will check on the wiring situation as soon as I can. Thanks.
  6. LinkedKube

    LinkedKube TechSpot Project Baby Posts: 3,481   +44

    well I guess taking to get fixed didnt solve your issue?
  7. jonathanreuter2

    jonathanreuter2 TS Rookie Topic Starter

    yeah that's what i've been saying...
  8. smaurer69

    smaurer69 TS Rookie

    You might be able to fix it in the bios under the hardware monitor tab or something. That does sound really strange though if he replaced it with the same exact fan. It sounds like your missing an extra lead for connecting the RPM sensor
  9. captaincranky

    captaincranky TechSpot Addict Posts: 11,700   +1,886

    Whaling Stories... Fact or Fiction

    The color coding of fan wires is, I believe universal.
    1. Black = Ground
    2. Red = + 12 Volts
    3. Yellow = Tachometer
    4. Blue = PWM (pulse width modulation) The processor & auxiliary fan speed
    control wire.
    You can connect the fan connectors (NOT THE BIG MOLEX TYPE) either three or four wire to either 3 or 4 wire fan headers on the motherboard. The plugs fit they just skip a pin. But, the fan will either run full speed or on it's lowest depending on which pin is missed, the fan's or the board's.
    It my Intel (and I can only speak directly to this type) board G965W (which has PWM control for the processor, you can tell the BIOS to not bother to detect new fans. However, I don't think you can tell it not to detect the processor fan. I'm not stupid enough to try that anyway. (Under Advanced>hardware settings). Unless you can tell me that the old fan took out the PWM board circuits and left the power headers intact (I believe that this could be possible, although not likely) Somebody's tellin' stories at the repair shop.
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