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left fan going out of control- can't find a cause!?

Hello, thanks for reading. regarding my 2012 mbp retina.

My left fan is revving up to extremely high speeds, randomly. I have scoured the net to find potential causes and solutions but nothing has helped so far.

I will say, even when running slowly it has a slight rattle/creak almost like the something may be rubbing. BUT this only highlights the speed when it ramps up, it is LOUD like a drone taking off and a light but high frequency vibration through the machine. I can sometimes tap on the left speaker/fan area next to the keys when it's going full speed and it stops (goes to the standard silent idle), for a short while.

so far, I have tried;

  • SMC reset,
  • full diagnostic test showing no issues
  • PRAM reset,
  • opened activity monitor and nothing is eating my CPU, deleted printers incase it was an issue with that, it's going full now as I type and I have over 85% idle. max used is 10% for the activity monitor itself!
  • full virus check just incase.

I have downloaded the mac fan control program to try manually set fan speeds. The right fan works perfectly and corresponds to my commands. As does the left fan when it is idling. Now, when it goes into this frantic mode and ramps up, The controller doesn't do anything at all. In-fact the real time monitor for it says its going really slowly (sort of looks like it malfunctions in reading), <2000rpm, when it is clearly ramped up from 2k through to top max speed!

The temperature sensors show nothing is extreme, all cores at about 52C, everything sitting between 35-61c max most in 40s, with only one thing (platform controller?) sitting at 61c.

I think I will replace the fan sometime soon anyway as it does have that tiny rattle, but I am concerned that something else is going on to cause this fan issue? I can't see how a rattling fan would also cause my machine to ramp up so high and loud, with no temperature issue or cpu load?

During writing this, the fan has done this a few times.

Can anyone provide insight or help?

Answered! View the answer I have this problem too

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Try replacing the fan, cant hurt


Have you noted any display anomalies?


no display issues as far as I can see.


@mayer I would've thought the same, but wouldn't both fans spin at full speed?

Anyway, there seems to be a fix for the MBP 15" Retina 2012 other than replacing the board or messing with the GPU.

I've tried two so far and had success.


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I'd replace the fan first since it is rattling. Or try this: remove it from the board, hold it with your two hands and press on the middle with your thumb as if pressing to make the fan click in place along it's axis. If you hear or feel a click, put it back and test your Mac again. If you hear/feel nothing, just go ahead and order a new one.

If you still have this issue with the new one, report back. I have a theory but you have to rule out a bad fan first.

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Ok, I shall have to get the right tools to open it up and give it a try. Will report once tried!


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Do you have any software installed that has control over the fan? Any performance enhancing software like msi afterburner? That might be the problem if any of the software is acting out...

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the issue was happening for a while before I installed a fan controller (mac fan control) to see if I could override it. The left fan doesn't respond to the program values I set when the ramping up begins. Otherwise I have no other installed control such as afterburner etc.


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aaron.swan will be eternally grateful.
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