Chosen Solution
I have a Mid 2012, 15” MacBook Pro (A1286 - with 820-3330B logic board). The problem is that the macOS can’t read the CPU PECI or CORE TEMPS. The fans are running at full throttle, kernel task reaching 600% and CPU usage is 95%, making the system super slow and unusable. Checked all the sensors using ASD, all sensors read OK, test passed, apart from the TIM test 75%GB test failing which I believe is a false error on these MacBooks. Ran “iStat” and “MacFanControl” to realize that I have no CPU Core or CPU PECI temps being read. But, if I boot the system from the Windows 10 partition, the fans are still high, but the system is completely fine. The CPU usage is normal and the system works as intended, but with just the fans always on high. Ran “MacFanControl” in windows, still no core temps, but ran “core temp software”, which showed all the CPU temps in control and within limits. To my understanding, I guess the SMC is not able to read the CPU Core or CPU PECI temps. Please help, thanks!
Did you have a liquid spill at some point?Did you try using an external bootable drive (with a clean OS install) to see if your internal drives OS has a problem? Most likely you’ll need to inspect the logic board both sides following this guide: MacBook Pro 15" Unibody Mid 2012 Logic Board Replacement and look carefully around the SMC chip for corrosion damage.
