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I have acquired a 2nd-hand mid-2015 MacBook Pro which I use connected to 2x cinema displays (the laptop itself has some screen damage).

When connected up for the first time I noticed it was going insanely slow (16gb 2.8ghz w/ Radeon R9 2GB) even compared to my early-2013 model with half the spec.

Checking Activity Monitor, I noticed kernal_task was using 400% of CPU (since then I have seen over 1000%). I looked up the cause and that it was overheating so opened it up and cleaned all dust out with blowers etc. to the best of my ability - no change.

I noticed using the laptop without anything plugged in seemed to be okay, so I initially thought having 2x displayport connections to screens was doing it. Since then I've discovered (like right now) I can have 2 screens plugged in and it's okay - then sometimes I add USB devices and it's okay - but when the system really starts working and needs fans - that's when things go bad.

So I installed iStat Menus and have discovered that my right fan is not operating (constantly 0rpm even when the left is 6000+ rpm).

So I'm wondering if a) this is the root cause (and not a symptom of the cause) and b) what I can do to fix.

Even though I cleaned it I did notice at the time its movement wasn't as smooth as the left - would cleaning help or would I need a replacement?

I've replaced MacBook components before so am quite confident in doing this if needed, but the fan isn't too cheap / available here so I'd like to know if I should expect further issues or what.

Thanks!

Mike

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Do you also notice the MacBook getting much hotter on the right side than on the left under load? This would confirm that the right fan is not working, so it wouldn't be just the sensor.

The kernel_task issue is a recently discussed topic and it is often caused by high temperatures. Take a look at this active discussion.

I would replace any broken fans and distribute external hardware that draws power and the power supply evenly between right and left ports.

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  • I don't notice heat greater than my other MBP, but I do believe iStat to be accurate that right fan not functioning. As this is an older model without USB-C, I can't charge from the right. I tried shifting all devices from left to right (including 1 of the displays - through the HDMI) and it didn't fix the issue at all. I'm wondering if the kernel_task is going way too far because the right fan not spinning. Original question still stands - fixable, replaceable or could there be a deeper root cause? Thanks for your help
    – Mike
    Commented May 11, 2020 at 13:53
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I opened up the laptop and carefully took out the right fan (following instructions from ifixit).

I cleaned the fan as best I could with blower and tweezers and carefully reconnected everything.

I switched the laptop on with the bottom casing still off and could see both fans working okay so switched off again and closed it up.

After booting it up MacsFanControl said both were now running (whereas before right fan constantly at 0rpm) and after some tests it's clear the kernal_task issue is no more and I'm running both monitors, 6 USB devices and processing heavy software and not even at half load.

Glad I tried the above before purchasing any parts or anything like that! It's 24 hours later now been throwing video rendering, gaming, three screens and more at it - and no problems whatsoever.

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