2008 Alu iMac - CPU fan runs high and noisy

[michaelwallmo]

howling fan in imac 24"

I have the same issue on my iMac but when I take the case off it working very nice the fans are running but you can hardly hear them but when putting back the case it starts howling again. Please can someone help?!

 

[fullojellybeans]

I have the same issue on my iMac but when I take the case off it working very nice the fans are running but you can hardly hear them but when putting back the case it starts howling again. Please can someone help?!

is the case screwed in when back on or is it unscrewed?

could be a few things.

1. a screw through a small cable, usually happens along the bottom area on the aluminums.

2. the cable that plugs in the camera is bad.

those are the only likely things that could cause this to happen when the case is "on"

 

[michaelwallmo]

is the case screwed in when back on or is it unscrewed?

could be a few things.

1. a screw through a small cable, usually happens along the bottom area on the aluminums.

2. the cable that plugs in the camera is bad.

those are the only likely things that could cause this to happen when the case is "on"

You suggested 1 & 2.

It was no 1!

When I first reassambled it I used every screw in the case. Later, when taking the case off and putting it back several times I used only four screws.
One of the long ones, just as you said, in the lower area shortened a tiny cord.

Thank you so much, it seemed to me that it had something to do with the heat and ventilation. Because it felt that when putting the case back without screws it worked an then after a couple of minutes I figured it was ok I put the four screws back and then it started. Not even then I had that in mind I only assumed that it took theese couple of minutes to heat up.I did not had that on my list until you told me!
Thanks again!

 

[NYarchitect]

Just wondering here.... It seems the hard drive on my Imac flat screen has gone bad. I had to back up and went to a friends to use his machine to do a target boot. We had some trouble starting the machine and had to do a power reset (PMU I think). We did that and....
the moment we started up the machine its fans started up at a speed I never heard or saw before- I say "saw" because a rather disturbing amount of dust immediately came out the top slot. Rather obvious evidence that the fans had never spun so fast previously- so much dust had been allowed to accumulate!!! So I am left wonder if the temp sensor or fan controls were always defective and my poor hard drive was left to overheat the 2 years and 9 months I have owned the machine.
I can say from experience that the machine was acting very much like a computer whose hard drive was cooking up- slow processes, more frequent hangs and freezes, and finally a machine which would not boot up- even in safe mode. Also, it has been very hot here in NY- the machine started going downhill two weeks ago, and gave out over the 4th weekend.
Defective temp/fan controls sound right?

 

[iMac72010]

error 4SNS/1/40000000 TGOH

Hi Richdave,

how did you exactly fixed your problem?
I have the same issue:
My CPU fan runs shortly after start witj 3900rpm, while there are no disturbing processes or high temperatures. I checked it with istatpro and smcfancontrol.
I run altough the Apple hardware test (aht), it displays the following error:

4SNS/1/40000000:TGOH-131.000

I found out that it is a faulty sensor, but which one exactly?

Hello people I have the same error code as well 4SNS/1/40000000 TGOH

My fan would would run normally and after about 10min it will get faster and faster, eventually, a grey screen will cover the screen and tell me to "Shut down the computer..."

How did you guys solve this issue? My iMac 7,1 is out of warranty willing to DIY.

Thank you

 

[Dadioh]

I have been reading my newly acquired service manual and CPU fan run on can be caused by a faulty PSU temperature sensor too!

The plot thickens just when I have ordered a new LCD sensor....

I just picked up an early 2008 iMac 24" and the CPU fan will run at 1200 rpm for a while and then every once in a while jumps to high speed. When I look at the temperatures through iStat Menus (one of my favorite programs) I notice that when the CPU fan is running normally the power temp is showing about 56C. But when the CPU fan jumps to high speed I see the power supply temp reporting as - So I suspect the power temperature sensor is flakey. Will do some more reading to confirm how to change it but thought you could benefit from this tidbit.