Q: Problem with Kernel Task - El Capitan

As an IT pro to another, let me run this by you:  I was onsite, and after driving >5 hours I swapped out my battery (my AC converter died) on my MBP late 2011 15", and tried to boot into my Win 7 bootcamp partition.  It booted, but the screen was black.  I used a Thunderbolt/HDMI converter and connected it to the TV where I was working (70" Samsung), everything looked beautiful.  Checked hardware monitor and my laptop display isn't listed.  I reseated all the connections, put the other battery back in, still black screen.  Reset SMC, PRAM, still black.  Tried a trick I found with google where I put the monitor to sleep, forced a reboot, still black.  I let the battery bleed down until it hibernated, plugged in, still black.  I'm about to swap it for another screen that I have with a broken bezel just to see if it's the actual screen, but I was hoping you may be able to shed some light on this.

Sorry we didn't resolve your issue.

Hey Badger,
No worries about the issue I had. I really appreciate all your help. I ended up just taking it to an apple service place since it was still covered by apple care. Despite the fact I've voided the warranty in at least 10 different hardware-related ways, it looks like they will be replacing the motherboard for nothing more than a 30 dollar service fee!

Anyway, as for you issue:
A 2011 MBP should be able to boot regardless of the battery, as long as it's plugged in to power. I guess I'm not certain, but I vaguely remember booting a 2010 MBP with the battery completely removed. Although the black screens may have initially been caused by a power/battery issue, I'm not inclined to assume that they're ongoing occurrence is power related.

Can you hear the hard drive kick on at all when you boot? I assume yes. But does it shut off when you get black screens? I'm not suggesting that the power cable to the HD is failing, but in my experience, older MBP's usually make little "writing/reading" noises if their actually doing something. Try paying attention to the HD sounds before and after the black screen and let me know if you notice a difference. We need to find out if the problem is related to important internal hardware, or just some faulty cheap internal display cable.

If the drive is operating regularly and you're still getting black screens, then your internal display cable or GPU is probably going bad. If it's the display cable, you're in luck obviously. But if it's the GPU... that *****! Mid-10 to 2011 MBP's have a known GPU issue. In fact they were "recalled" without customer notification. Or.. "owner notification", w/e. You essentially had to have already had the problem and sought help in order to get a free replacement (whether you had apple care or not). If you're able to boot into safe mode or from a disk you may be able to find crash reports. If you see a "GPU Panic" report anywhere, you're screwed. And by screwed I mean, even if you do get the macbook to boot naturally with its own drive, files, and respective OS partitions, you'll never be able to run photoshop, imovie, or Left4dead2 () ever again for more than a matter of minutes, and you will have to run GFX card status to disable your discrete graphics and force your integrated card at all times. 

When you hold option at boot, what happens? You're able to select which partition to boot from? Do you have a backup? The first things I do when I come across weird situations like this are:

1. Get another MBP, take the HDD out, plug it into the MBP that's having issues, try to boot.
2. Take the HDD out of the Macbook Pro that's having the issue and try to boot from the drive with another MBP. You can also use an iMac or mac desktop. In fact, you should be able to use really any mac computer. You can also boot from your drive externally if you have a dock.
2. Remove one of the sticks of ram and try to boot normally.
3. Put the stick you removed back in, remove the other stick, and try to boot normally.
4. Run Apple Hardware Diagnostics via disk or flash drive.
5. Unplug all easily-unpluggable motherboard, hard drive, display, power, sensor, and optical drive cables from the inside of the MBP and plug them back in, then try to boot normally.
6. Does your model have a CD drive? If you have a sata to microsata converter you can try booting from the drive via your optical drive's sata, rather than your Macintosh HD sata.

I know you probably don't think the issue is related to the hard drive, but if you can manage to boot safely from the drive on another unit, you will have definitely narrowed down the cause of the problem.

Let me know if any of this helps!

It boots fine, I can even play iTunes (because I can login and use the media keys with no screen).  As I said, when it first happened I connected it to an external display (70" Samsung) and everything was beautiful - Bioshock Infinite looked great, but ran like crap because 4K / ATI6750 w/512MB 8(.  I got one of those 2011 MBP's cheap with a faulty nVidia GPU (shame too, it's a 1GB card) and was able to boot it a few times.  I tried to lock out the discrete card but didn't have any luck, even with GFX app.  Now it's spare parts, and I did swap out the screen a few months ago after I broke the bezel on mine, and it's where the spare battery came from.

So yeah, it boots normally, but the computer isn't seeing the screen at all.  It probably is the cable but I've tried with the screen at all angles and nothing, it just stays black like it's not even connected.  Weird, since I didn't even touch the cable when I swapped the batteries, and it worked perfectly moments before.

O yeah, I also replaced the drive with a 1TB hybrid drive, replaced the Superdrive with the old 750GB as a Time Machine backup drive (not concerned with backing up the 250GB bootcamp partition - all my saved games are in the Steamcloud, and that's all I do with that other than the occasional bit of work/MS Office which I immediately email to whoever is still forcing me to use Office), and upgraded to 16GB DDR 1333 ($75, thanks newegg!).

So, you can use the mac with an external display? The problem is simply the built in display?

Exactly.   Desktop looks amazing in 4k, so even though I forgot to check, I'm pretty sure the discrete card is good.

Not seeing my model in Resources (MacBookPro10,1).   I didn't boot in safe mode yet.. does that make a difference?

Still not there.   Any other ideas?

For me, the issue was logic-board related and required a replacement. My model (14,1) also did not show up in the list.
If you have any other working apple computers laying round, try swapping the hard drives. Put the working mac's hard drive in the mac that's having the kernal task problem. It should boot fine. You can even put a macbook or macbook pro's drive in an iMac and it will boot as if your iMac were your macbook. Anyway, if the kernal problem still happens when booting from an OS on a totally different drive, then the problem is surely motherboard related.

Probably not the logic board.  Doesn't happen (that I've noticed) when I have the laptop at work.   Has to be one of the externals at home then.

This is not a hardware issue, it is purely a firmware issue related to Yosemite and El Capitan. If you have already attempted to reinstall your operating system, next step would be to make a Genius Bar appointment Apple and have restore computer back to factory settings. Issue will be resolved. You can attempt to restore from backup, but i've noticed that the issue returns after, so the for sure fix will be to restore back to factory settings in an apple store and setup the unit as new, then you can "Enter Time Machine" and manually restore data.

Worked for me. My system was running very slowly. Fans were running full speed. kernel_task was consuming all of CPU. If it holds my mac is back.

Thanks BMonkey.

This was on a SkyLake iMac 5K. Resetting the NVRAM solved the problem.

What made me optimistic it would work is that the NVRAM Apple KB article mentioned speaker volume might be one of the parameters that would have to be re-configured after NVRAM reset. My external speakers (connected via USB) had been randomly cutting out; power-cycling them fixed the problem, but was clearly not its cause.

Kernal_task went from top CPU process, consuming 20-70%, down to ~1%.

Thanks again!

Fixed... I finally found the problem why kernel was taking up so much bandwidth, I downloaded a program called Silverlight.dmg once I trash this program it fix the problem.

I really hope this helps anybody else that is going through these massive downloads taking a lots of bandwidth

Thanks for the tip! On the same page with all the same problems. However, when I get to the extensions resource folder, my Model Identifier (MacBookAir6,2) isn't in the resources list. (Highest is MacBookAir4,2). Any suggestions how I can proceed? Thanks!

Silverlight was required to use Netflix on Safari and was the only reason I was forced to restart my Mac EVER (it's Microsoft, so... yeah).  I switched to HTML5 in the Chrome browser and uninstalled Silverlight and renewed my vow to keep my Mac MS free.