IMac cpu fan running at full rpm

hi all
A few days ago my cpu fan started running flat out. I have done the smc or whatever it is caled reset thing where you unplug the cored ect.
I have done the hardware test with no bad results.
I have checked activity monitor for cpu usage and there is nothing unusual there, so I can only guess that the cpu temp censor is faulty.
I should also add that this machine has been running non stop since mid 2007 , with the exception of the odd blackout and restart, thats pretty amazing i think.
maybe its time has finally come ;(
any clues ??
thanks

SMC is firmware and OS X is software, which has nothing to do. Furthermore, you are using a very old iMac, so SMC should not have been updated with OS X 10.10.2.
If you have tried a SMC reset and it did not work, run Apple Hardware Test (make sure you choose an extended test) to see if there is any problem with a temperature sensor or anything like this -> Using Apple Hardware Test - Apple Support
Note that you may need the DVDs that came with your Mac in order to run it. If you get an error at the end of the test, please copy it here.

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Hi again Miriam,
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I have an early 2008 imac running upgraded ram, Mountain Lion 10.8. I hve a CPU fan that is running at 3900 rpms. I have downloaded the SMC fan control, I have tried doing the option,command p,r. I have done all the shut down procedures. I tried ro restart in diagnostics mode but it wont restart in diagnostics mode (I tried using option D as well as just D on start up) I downloaded and tried using a shell app command with Automator that is suposed to force the fans tor run at a particular speed ie: 1200,1500,2400 etc. but it does not work. I do not have a start upd disc for Mountain Lion. Don't know what else to do.

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mende1 wrote:
Welcome to Apple Support Communities
It's clear that there's a problem with your Mac, so the best you can do is to make a backup of your files and take your Mac to an Apple Store or reseller to get it repaired.
If you want to know what's failing, run Apple Hardware Test > http://support.apple.com/kb/HT1509?viewlocale=en_US&locale=en_US
In your iMac, Apple Hardware Test is included in the Mac OS X Install DVD 2, so insert it and hold the D key while your computer is starting. Disconnect all peripherals except the keyboard and mouse, choose your language, mark the box to use the extended mode and start the test. At the end of the test you will probably find an error, so copy it here

IMAC G5 fans running at high RPM

Hello,
I have a 20" G5 iMac and just had the motherboard replaced under warranty. Since the replacement my fans will start to run at very high rpm's fr no reason. It will happen even when the computer is not being used and no applications are running. It is currently at:
CPU 122 degrees
CPU fan 2996 rpm
HD 124 degrees
HD fan 4178 rpm
System fan 3098 rpm
I have called applecare and they had me do several resets which seemed to help for about 1 hour and then the fans have ramped up and not gone down in the past hour. This last time I was watching TV and heard a noise from the computer and low and behold it was the fans. Nobody was working on the computer and all apps were closed. I bought this computer in September 2005 and have had 2 lcd's replaced and a logic board replaced. I am getting frustrated with this, my first, Apple computer. Does anyone have an idea of why the fans are running so high? I never had a problem like this with my old logic board.

Have you looked in Activity Monitor to see if any applications are causing the fans to run? Applications/Utilities/Activity Monitor.

ODD and CPU fans running at high RPMs

Hello!
My iMac's ODD and CPU fans are running at unusual high speeds. If I turn the computer off and on they usually run at a normal rate but start rotating at around 3700 RPM very quickly (about 1-2 minutes after the OS X has started). The CPU load is not unusually high. The HDD fan is not affected.
I have tried SMC and PRAM resets multiple times.
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Intel Core i7 2,93 GHz
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SMCFanControl reports the CPU fan at 3900 RPMs (full blast) but what is it trying to cool? The temperature is 27 degrees celsius (80° F), Activity Monitor says 93% of my CPU is idle. I've done all the normal SMC/PRAM stuff and it seems that my CPU temps is just fine. Something needs to be replaced.
Sensor
Fan
DC Power Supply/SATA/Inverter cable
Also, yesterday it repeatedly shut down and restarted itself over and over and over until I unplugged it.

I realize that Eric. However, I am currently unable to: https://discussions.apple.com/message/21827955#21827955

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Hi,
For about 3 months now I've had a problem with my iMac where the CPU fan runs at full speed from start up, until I turn it off. It is extremley noisy and frustating.
I am pulling my hair out trying to fix it.
So far I have reset the SMC and PRAM and downloaded fan controllers. I've also opened it up and checked the sensors and cleaned out all of the dust, but this annoying problem still persists.
Is there anything else I could try that could fix this problem?
Thank you very much.

Thank you
I have tried to run the AHT many times, but for some reason I can't get it to work. I even tried booting it from the insitallation disk which someone else suggested.
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IMac CPU fan speed

I recently just had Apple look at my iMac, reason being for the glass to get cleaned on the inside as well as the LCD to get replaced. Waited a week, went and picked it up, only to be disappointed by the fact that the LCD wasn't replaced.
Called Apple, they sent a certified technician to come install my LCD panel. Where he came from, was farther than the closest Apple store near me. Anyway, he came and replaced my LCD, and we tested it to make sure everything was good. It was, and I asked him to leave the glass on, since I was going to be cleaning the insides out. Apparently 3 years of dust accumulation looks pretty gross on the inside .
I ended up taking the motherboard out, to clean the heatsinks and to reapply thermal paste on both the GPU and CPU. They did have an excess amount on, but for the most part was done A LOT better than my early 11 17" 2.3 i7. I ended up taking the hard drive out and swapping it for a 80gb Intel x-25m and tagging the temp sensor on it.
After putting it all together, I noticed that the CPU fan runs around 3700 rpm. I tried resetting the SMC, no luck. I can use fan control or SMC and turn the CPU fan up, but it won't go below the 3700 mark.
One thing to note, is that I have NOT put the glass back on, as I do not have any suction cups. I do know that I plugged everything in correctly, as well as taking the HDD temp sensor from the 1tb stock HD to put on the SSD I installed.
So what could this be?
ps. The Apple certified technician at the Apple store straight up told me that the iMacs DO NOT use thermal grease (I asked him if he could reapply some). HAHAHAHAHA what a dummie.

What kind of thermalpaste did you use? some types of processing units need special kinds of paste.
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My 3 month old iMac 24" has just started having fan problems.
Before I went away on a training course, it was working fine. Left it switched off at the outlet for 3 days, now the CPU fan runs full speed after the iMac has been switched on for 15 to 20 minutes.
CPU temp is 24C, CPU heatsink is 28C. Ambient is 17C. CPU fan is 3600rpm. Other fans are normal.
CPU usage is less that 10%. Only Safari is running.
I've tried resetting the SMC - left all plugs disconnected for 15 minutes, reconnected mains power for 15 minutes, reconnected USB, then switched on.
Still the same - OK for 15 minutes, then CPU fan runs full speed.
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I tried again, following your instructions exactly. It seemed to work, running normally for about an hour.
I left all the USB devices unplugged, except for the keyboard and mouse.
I then shut the iMac down, but left the mains power turned on at the wall. When I switched it on again 2 hours later, all was OK for 15 minutes, then the CPU fan ran at full speed.
Shutting down for a few seconds fixes it for another 15 minutes.
I'm wondering if it's a software problem, although I haven't loaded any apps recently, apart from a few monitoring programs since this problem appeared.
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I suspect you have hardware problem with a fan sensor. Doing a software install will not help the machine needs to be taken in for service. If you run Apple Hardware Test in Extended Mode it should reveal the error code. If it does not then run AHT an additional 2-3 times to be sure in Extended Mode. Each pass will take about 30-60 minutes.

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Thanks

Hello irisfailsafe
Welcome to Apple Discussions
Reset the SMC > http://support.apple.com/kb/HT3964
+1. Shut down the computer.+
+2. Unplug the computer's power cord.+
+3. Press and hold the power button for 5 seconds.+
+4. Release the power button.+
+5. Attach the computers power cable.+
+6. Press the power button to turn on the computer.+
Dennis

Fans run at full speed

As in subject, my brand new iMac Aluminium 20" 2GHz has a problem: fans run at full speed...
After reset of PRAM or SMC, fans start slowly (1200rpm) but rise ti 3500rpm after few minutes and they don't change until a new restore of SMC.
cpu 3-4%,
no apllication opened,
nothing in dashboard.
What's happen?? I've never had a problem with my mac!
PS: sorry for my bad english, I'm italian!
cerion
Message was edited by: cerion86

Hi, just an update -
I ran the Apple Hardware Test on startup, and it returned this hardware error: 4SNS/1/40000000:TpoP
I brought my machine to the Apple Store where I bought it and they ran their diagnostics and said there was nothing wrong. So when I picked it up we booted it up in the store and the fan was about 1200rpm, no problem. We ran the Apple Hardware Test in the store and it didn't give the same hardware error that I'd had before.
So, I didn't really have any ammunition to press them any further on it and for the last week it's been fine. I had the fan race on me again last night but I hope it was an isolated incident.
As for downgrading to OSX 10.4, I'd consider it but I don't feel that I should have to do that to make my hardware perform correctly.
Re. smcFanControl, I thought the purpose of that is to make the fans run faster/more often, but if anyone's used it to stop them from running too fast/too often I'd be glad to hear from you.
Maybe the 10.5.2 version of the OS will take care of this problem, if indeed a problem exists.

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When I started it up again, it started making the same noise with the exhaust fan running at full speed. I installed SMCFanControl and I see that the CPU is barely warm - 35-37C and yet the fan is running at full speed. I looked at the CPU/HDD usage and there is barely ANY usage (~90% idle). Nothing out of the ordinary. So it definitely doesn't seem to be a heating issue.
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I don't know what that code means for sure, but it sounds like one of the temperature sensors may have died, so the fans just run at full to cool.
I would take it to the apple store.

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I play a lot of games, including this same one, and I have never seen the GPU this hot before, and almost never hear the fans running so loudly and so rapidly. (I can't even recall a time when I could very clearly hear the fans running.)
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CPU: 52
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Mem Controller: 60
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If you're running ESET Cybersecurity you may need to upgrade. Older versions have been causing a crash in the Launch files which means reportcrash constantly triggers (drains battery and kicks in the fans).
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IMac cpu fan running at full rpm

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