Very low CPU temps, resulting in fan stuck at low rpm

[t0yz]

Hello,

I'm having this problem lately with the CPU temp (not the cores, these temps are reported correctly and are into the low 40s on idle), it's most of the times detected as low as 1-5 degrees (Celsius). I did not made any changes I can remember other than replacing a faulty HDD with new SSD/HDD (but I cannot guarantee this was the start of the problem). It just started to happen (I have AIDA64 OSD running).
Important mention: the CPU sensor is not stuck when it indicates low temps, the temps go up on load, but they're 15C or so lower than normal.

This is bothering me because I use a Freezer PWM cooler set on Turbo on BIOS. The fan needs to go as high as 2500-2800 rpm to keep the CPU cool when it needed to work on the hot ambient here, but now, because the low CPU temp is detected, the fan sits lazily at 1100 rpm and the cores go up to 65C (tested with IntelBurner). What's even more annoying, is that sometimes the correct CPU was reported after a reboot (this is not happening any more - the temps are wrong for good it seems) and the fan immediately starts working correctly again, but it never lasts. Everything on the motherboard is correctly seated with Arctic MX-3. I did a fresh reseating for the Arctic cooler, but it did not help.

Additional problems I have noticed: the CHA fan is no longer detected, albeit it's working OK. A wrong DRAM reading appeared out of nowhere during my attempts to repair this issue, detecting a 2.02 V - incorrect, as the RAM sticks are working at 1.8 V.

I have also tried reflashing the BIOS to older versions, resetting CMOS, overclocking the CPU up to 3.5 GHz, everything in an attempt to get the sensor IC unstuck, but none worked.
Speedfan is not a possible resolution - I cannot control the fan on my MB with it.

Is there any way I can "reset" the sensor to its former, correct behaviour? Please help, I'm getting desperate here, as the only way I can tackle more demanding tasks other than browsing is to disable the Q-FAN BIOS option and let the fan always work at 2700 rpm - it's like having a blowdryer in your ears all the time.

Thank you!

E7200 2.53 GHz, Asus P5Q (2209 BIOS), Kingston 2x2GB DDR2-800 5-5-5-18 1.8v, Asus EAH4850 512MB 625/993, 23" Fujitsu-Siemens LSL 3230T, Corsair Extreme SSD x64/Samsung Spinpoint F3EG 1TB SATA-II, Windows 7 SP1 Ultimate x64

2.53 GHz, stock:

3.16 GHz, OC:

DRAM wrong entry:

 

[VirtualLarry]

65C for Core2Duo core temps aren't that high. Mine are 80-85C right now, running DC apps.

If you want your CPU fan to run at full speed, disable "smart FAN" in BIOS.

 

[Tim]

65C for Core2Duo core temps aren't that high. Mine are 80-85C right now, running DC apps.

If you want your CPU fan to run at full speed, disable "smart FAN" in BIOS.

Did you even read the OP's post?


OP... I hope somebody here helps you figure this one out. The last time this happened to me, I gave up and finally just replaced the motherboard. (which solved the issue) My hardware profile was much different than yours, with the only commonality being that we both had ASUS motherboards.

 

[t0yz]

Thank you for your answers. Yeah, I know it's a sticky issue and that the MB might be on its way out, I'm using computers for more than 20 yrs now.
I'm not concerned about the temps being too high, but too low. Also, this problem seem to have started a few days ago, and the CPU temp went lower and lower as time went by, so I didn't even notice it until I had to run some demanding apps and I failed to hear the fan kicking into action.

Development: I took the board out, and treated it the way I end up treating any electronics after the "brain" solutions expire: light mechanical shock Gave every chip on the MB some tickles. After that, I took the battery out and resetted CMOS once again.
What do you know... the CPU temp seem to be back on track (approx 12-15C lower than the Intel diode reads), fan working again obviously, and DRAM erroneous entry disappeared from HWMonitor.
I'm still very concerned about this, and I'm actively monitoring the responses on this thread to see if there's a permanent solution, as I have a feeling this lucky event won't last long.

 

[tommylommykins]

if this happens again, you may be able to get away with plugging the CPU fan into the back-fan socket of your mobo.

 

[t0yz]

if this happens again, you may be able to get away with plugging the CPU fan into the back-fan socket of your mobo.

I'm not sure I understand what you mean. The CPU fan is plugged into the 4-pin CPU_FAN connector. Other fan connectors on this MB model: CHA_FAN 1-2, PWR_FAN (3-pin). Below is the layout for a P5Q PRO (couldn't find the Vanilla model that I have), which has an additional PCIe x16 slot.

 

[Tim]

He means just plug your fan into one of the other slots besides the PWR_FAN slot. Have the fan run at full speed, or some other bios set speed from a different fan port such as the CHA_FAN1 or CHA_FAN2 spot (FAN1 would be your best option)

 

[t0yz]

He means just plug your fan into one of the other slots besides the PWR_FAN slot. Have the fan run at full speed, or some other bios set speed from a different fan port such as the CHA_FAN1 or CHA_FAN2 spot (FAN1 would be your best option)

I can run the fan at full speed from CPU_FAN with no problems if I disable Q-FAN, but it just hurts my ears at 2700 rpm. The problem comes from the Winbond sensor which gives false readings for the CPU temp, which is used by the PWM. It is a possible that the PSU is faulty, as I saw the CPU temp dropping when the GPU went under heavy load - just like the sensor chip was starved or something.

When I have money for a decent PSU, I'll replace it and see what happens. Until then, I guess I'm stuck with the CPU fan at minimum rotation, load or idle. Lucky me it's almost winter and the temps are very cool here, so the CPU almost cools itself passively.