Fan running at full speed, CPU throtled

"This is most likely your trackpad. Since you replaced your board and HDD cable there is not much left. Before replacing your trackpad, download Macs Fan Control and see what your battery temp sensor is reading. Normal is anywhere from room temp and up but nothing over 50. Your looking for some crazy reading like -144 or something of that sort. Your trackpad has a temp sensor and is a fairly common issue.

Update (09/08/2017)

Also check your HDD temp in the same program. Again... Look for crazy temp values."

Hi I think the pram or smc reset fixes this maybe it's a pref if the first two don't work try restarting in recovery mode command r... and see if it fixes it that will tell you its software if not you could be a goner but I'm not a tech at all!!! But I did have this on one or more of my mbp

Hi there i have the same mac and I have the same problem but power button don´t works the light on keys don´t work the fans are 100% cpu kernel task uses 200% cpu. I allready change the disk for 1 ssd install last version of OS sierra but no luck I try tu update smc it says that update but when i see version is the same. the power button works when i made key combination like option + comand + power so is not hardware fault . i have the web cam broken can be from there? is there any solution please help me this is my first mac and Im regreted all ready

"I have a more cynical and conspiratorial answer to this. I have exactly the same problem with my 2012 Macbook Pro. However, this only happened after my machine would not switch on at all.

I was told that maybe taking the back off and disconnecting the battery for 60 seconds would solve the problem, which it did. My Macbook started up with the power button for the first time in weeks, and I was very grateful.....

That is until I realised the computer no longer recognised the battery, the fans suddenly started doing 6200rpm, and something called kernel.task was using 300% CPU time, resulting in my machine now being mega-slow.

Apparently this is a panic reaction to temperature sensors reaching 100C or thereabouts and designed to prevent the user from commencing any activity which might push the temperatures any higher.

All very logical you might reply, but I do not believe this was just coincidence. After all, I paid for my laptop years ago, and it is well out of warranty. If I choose to fry my CPU, or disconnect the battery, or interfere with any component on the motherboard, that should be my right without any built in codes by the manufacturer to prevent me from doing this.

If we could prove that this is a deliberate ploy by Apple to encourage the purchase of replacement parts, or expensive and un-necessary repairs, then in my view that is a deliberate fraudulent activity in order to increase profits; and needs to be tested in the courts; as millions may have spent money they didn't need to.

There must be a file somewhere in the system folder, which kernel.task is using in order for it to continually access a simple routine (review date/time for example) repeatedly; and if this was moved to the trash the process ought to cease on a re-start. However, I would not care to beging trashing systems files, and I might not have enough access privileges to do so anyway.

If anyone has any idea of the likely name(s) of anything which could be the culprit, I would love to know."

The problem could potentially be the battery as well. If a Mac doens't detect an internal battery properly, I have found that they will throttle the CPU. A battery replacement wouldn't hurt to try, especially if yours has a lot of cycles already.

"Here is a photo of my temperature readout. The 128C is what the system is saying, which is nonsense as the air from the fan exhaust is cool.

The two other temperatures are from an app called Temperature Gauge 4.1 which is set to give CPU 2 Core and CPU PECI temperature sensor readings."