Model A1311 / Mid 2011 / 2.5 & 2.7 GHz Core i5 or 2.8 GHz Core i7 Processor

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Diagnose for iMac 4MOT/4/40000002:CPU-143

I purchased CPU Fan here, but it keep the same result as of 0 rpm. Then I run Apple Hardware Diagnostic, and the subject was the result. I do not know what could be the issue here now. Any suggestions?

Update (09/13/2018)

This is the screen-grab from my last chat to OWC Technical Support.

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已回答! View the answer 我也有这个问题


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Have you changed the hard drive?

Have you altered the system in any way, or, removed the logic board?

Dan, Yes I removed the logic board to replace the Video Card.

Did you fix the problem ? Because I have the same issue with my Imac mid 2011

You may want to create your own question as Mark had a few different things go on his system.



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TLTR; I already forgot this. Sorry to my late response.

Actually I’m using my iMac now for awhile now. I can say, 5 weeks from now.

In my deep observation, after I receive this error. I was thinking if the CPU fan was not working before my Video Card died and also damaged my HDD.

Please follow this link: White Screen of Death after booting up at Recovery Mode

So the case was, Before my VC died, I experience a heavy blower running on my iMac everytime I open it. So I have to reboot it and the blower will run back to normal state. Now, the blower that runs heavy here is the ODD Fan.

ODD Fan in my observation, is also the blower of the Video Card Heat Sink.

Now, after I ordered new CPU Fan here at iFixit including additional 8Gb of Ram (I have a thread as well for my RAM Upgrade), I started this thread in relying of might be the case was a defective CPU fan. But after running a System Diagnose this was the error. I am not a Mac Wizard Tech but I have a background of Computer Technician, so I have to evaluate everything going on here at my iMac to avoid very expensive costs to revived this machine.

All Check:

  1. I test all the wirings and connections are all ok and responding = ok checked
  2. found some ground wirings are exposed due of the cover was breaking down = covered with electrical tape
  3. replace cpu/gpu thermal paste = ok done
  4. test all the fans if are all running fine = ok checked, except CPU fan socket

I deeply look to the board and see that there’s a little thing that “seems” busted, but I don’t see it clearly if it is busted or just a wire that got exposed. Overall I ignored it for now, I don’t want to go further to mess more the logic board.

Photo Fig. 1

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(click the photo to see my red circle)

The final decision was a suicide logic board. But before that, I check and google if there’s a way to manually control the fan and see all the temperature inside hardware while I’m using the iMac. Yes there is. I download the copy of Macs Fan Control (google it and it is free).

Warning: This might be dangerous, but I do accept the risk and to risk my logic board (or even my iMac) if this experiment gone wrong.

I start the operation to tap the wire of my CPU fan directly to the wire of my ODD fan*.

After this successful fans wire tapping, I leave and observe the unit for a day or two without turning it off.

And it seems running fine. Though my initial investigation here was the fans that are oddly runs fast sometimes and sometimes not.

Here’s the condition I found:

ODD fan rely on the Optical Disk Drive temperature base on the sensor. And the CPU fan sensor also respond to the CPU heatsink temperature. Now, since the CPU fan wire was wired tapped to the ODD fan, the power supply that run to the ODD also get equally to the CPU fan. However, due of the sensor activity of the CPU fan, it filter the power**.

*I will upload soon a picture of what I did here.

**You will hear this fans loudly running if you will not configure your fan via Macs Fan Control app.

NOTE and WARNING: Again, I repeat. I do this in my own risk and have a background knowledge of what I am doing, if you are not expert or do not have a background knowledge, please consider buy a new logic board instead of this.


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Hey Mark, also considering wire tapping the CPU fan to the ODD fan since I experience the same problem. Is it still working? Could you provide a picture, or a more detailed description how you have done this? Thanks a lot! Andreas

I'm sorry for the late response.

Yes, it is still working and smooth as new.

I will upload photos soon.

Ok, you need to follow the wirings of the ODD fan to be able to work the CPU fan. From ground to power lines, etc.. Once you have the tap successfully in place (calculate and measure the distance of the wire tap from ODD to CPU, because too long will give you problem putting back the LCD), then put the CPU sensor back to the socket and run the mac (i didn't cut the wirings here of the fan, i leave it as is). At first you will hear the ODD fan blows loud, here you will need to download the Macs Fan Control and tweak the speed of the fan depends on your application. I run custom value here for ODD fa "3500", while "2500" for my CPU Fan.


This problem can also arise with a changed hard drive or solid state drive, as @mayer said too.

The next step is replacing the CPU fan.


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Not time to recommend this yet.

@mayer Just saying, you never know what a user has done!

@mayer edited (dang sorry for like 3 tags)

@ajcooke01 the old CPU fan was not working, so I decided to purchase CPU fan here and replace it, but I still see 0 rpm on my sensor and sometime it run 143 rpm and get back to 0.

previously yes, I replaced the hdd and video card.

@danj @mayer I think you guys can take it from here, and thank you mayer! I received a nice email from Blake Barth that absolutely made my day. Thanks so much!


So, you’ve replaced the hard drive, CPU fan, video card?

Did you use an OWC Thermal Sensor to take care of the fan issue? Apple use proprietary hard drives on this model and later models to prevent users from working on their own machines. Usually not doing so will result in a run away fan.


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No didn't use one as I have follow one of the guide here for HDD replacement and that was way back 2016.

My video card died last June 9 and got a replacement last week of August. Then realized that my back panel went hot, and discovered that the CPU fan rpm is 0. I check fan noticed all wires skin peeled off, So I ordered a CPU fan replacement and replaced it after, but still the same result. Logic board is working fine "I guess" but not so sure, though I can still boot up to my OS.



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