Question Case fan speed stuck under 1000rpm ?


Oct 1, 2014
My mobo is a Gigabyte GA-970A-UD3P. I have tried 2 different 4-pin fans, and I have also tried every configuration in the BIOS auto/silent/manual with .75 to 2.50 PWM value per °C. No matter what setting I choose, the system fan 1 never runs higher than 1000rpm, which is odd because every other fan is running over 1000 rpm. Admittedly, my other fans are DC 3-pin, but they adjust according to system temps. So my question is this ... Why is my 4-pin sys_fan1 stuck at around 700-800 rpm?

I took a look at my mobo manual, I will upload a photo, but from what I am seeing the 4th pin isn't a PWM speed control pin, it's just a 'reserve'. Well, what does that mean? It's like an only backwards compatible 4 pin for DC fans with no PWM signal. Can anyone explain this to me? Is there anyway I can control the fan speed without buying a new 3 pin fan?
Are current 4-pin fans not compatible with my mobo's 4-pin sys_fan1 header? There's no option to select voltage control mode for the sys_fan1 like there is for my cpu_fan. Is this some weird AMD only thing?

The system fan 1 pins are as follows: pin 1 ground, pin 2 +12v/speed control, pin 3 sense, pin 4 reserve. Cpu_fan is same but switching 'reserve' pin for a speed control pin.(I am using bios voltage setting to control cpu fan speed). Sys_fan2/pwr_fan are ground, +12v, sense.
I hope that makes sense. Any questions, I will answer as soon as I can!

*** I am unable to upload a picture from my google drive because idk. So maybe I have 2 issues.

Thank you for your time,
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If you have PWM fans in your build, I'd advise on getting a PWM fan splitter or a hub to tether to the CPU_Fan header and wrap up the cooling aspect of the build. What BIOS version are you working with on the motherboard at the time of writing? If you're interested in managing 3pin fans while on a PWM fan hub, you can look into this Phanteks fan hub.

Make and models of the other fans?
motherboard manufacturers do not alter the fan headers' pin alignments that i have ever seen.

either you have some ancient board from before PWM was prevalent or just some very cheap junk that is not designed for modern uses.
tried every configuration in the BIOS...
other fans are DC 3-pin, but they adjust according to system temps
then it is set to a "DC" mode and PWM fans will not be controlled in "PWM" mode.

your best option would be to upgrade to a modern board with better options.
but you could also have an entire PWM array following the CPU_FAN header as @Lutfij suggested.
am unable to upload a picture from my google drive
using IMGUR as the image host and inserting with default 'Ctrl+P' allows images to be viewed within the thread.


That mobo's fan control features are from early in the introduction of 4-pin fans and do not include items common now. Moreover the labels used in the manual on p. 14 can be confusing.

First, some quick things about fans. Older fan have 3 pins and the ONLY way to control their speed is by varying the Voltage supplied to the fan on Pin #2 - from 12 VDC for full speed down to about 5 VDC for slowest speed without stalling. The new 4-pin fans are supposed to receive from Pin #2 a constant 12 VDC supply, plus the new PWM signal from Pin #4. It has a special chip that uses that PWM signal to modify the flow of current from that 12 VDC supply line though the windings to control speed. Connect those fans each to the matching mobo fan headers that use their correct control signals, and they all work. But mis-matching can be done. Plug a 3-pin fan into a 4-pin header and it will always run full speed because it gets a fixed 12 VDC from Pin #2, and no PWM signal from pin #4 that it cannot use anyway! You DO get good cooling but no speed control. Plug a 4-pin fan into a 3-pin header and it gets no PWM signal so its chip cannot modify current flow. BUT the Voltage supplied on Pin #2 is VARIED, so the speed of this fan IS controlled this way, even if not ideally from a technical standpoint.

Your mobo's CPU_FAN header appears to be a true 4-pin one using the new PWM Mode of controlling its fan. You say your mobo allows you the option for this header to choose Voltage Control Mode, but the manual does not show that. Is that true? IF it is, and IF your CPU cooling fan really is a 4-pin one, you should use PWM Mode for this header.

The Manual I see for that mobo shows Pin 4 of SYS_FAN1 as "VCC", which is not clear. There are two possibilities for this header. It MAY be a true 4-pin header using PWM Mode. In that case it should be set to Normal Profile. (The only way you can make manual settings via a Slope PWM setting is to choose the Manual Profile.) I note the manual claims this header uses the CPU internal temperature sensor for this header, but that may be a typo. Alternatively, this header that has 4 pins may actually be a true 3-pin header using the older Voltage Control Mode. As I said above, that STILL will control a 4-pin fan's speed, so such a trick is not obvious unless you start trying to use a fan Hub. Assuming this header IS exercising control of its fan's speed, it will NOT tell that fan to go up to full speed until the temperature sensor says temp is too high. If you try to force it manually with a Slope PWM setting, that can be done ONLY if you switch to Manual Profile.

According to that manual you have misunderstood the SYS_FAN2 and PWR_FAN headers. The labels indicate that both are 3-pin headers that do NOT attempt to control fan speed at all. Their Pin #2 is labelled "+12V", indicating it is always that way. You say these fans are running over 1000 RPM, and then you say their speeds are being controlled by the system. Why do you say "controlled" when they are running fast most (all?) of the time?

Few people remember the PWR_FAN header, which you have. In its original intent, it was for one purpose only. Over a decade ago some PSU's were supplied with a set of wires coming out and ending in a normal-looking 3-pin fan female connector. It was to be plugged into a mobo PWR_FAN header for the sole purpose of sending to that header the speed signal from the fan inside the PSU so you could see that. This header does NOT make any attempt to control the PSU fan's speed, nor even to power that fan - the fan was already powered from within the PSU. So if you do NOT have that set of wires coming from your PSU, you were supposed to ignore that header. Then many mobo makers modified that, and connected a full 12 VDC to Pin #2 and Ground to Pin #1 of the PWR_FAN header. Then you had the option of plugging into that header a spare 3-pin fan for extra cooling somewhere, allowing for the fact that such a fan would always run full speed - no control possible. That is exactly what the manual shows for the PWR_FAN header. It ALSO says the same for the SYS_FAN2 header which may be true or may NOT - we can't tell if the manual is wrong. But the labels for both those headers claim they do NO speed control.
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