Chosen Solution
Apple diagnostics came up with a PFM006 error on this iMac which points to the SMC controller. SMC reset does not fix the issue. TG Pro lists the CPU, HDD and UNKNOWN as possible failures for temp sensors. I have not opened this system up but the previous owner did have the screen replaced at one point. Fans run at full speed unless the computer is in sleep mode, they can be controlled by TG Pro. TG Pro was listing all temps as normal, then yesterday it came up with only the HDD listed saying that no fans were installed. Kernel Task floats around 200 - 300% consistently, which according to Apple is a safety feature to prevent damage to the machine when temps are out of control. Clean install of High Sierra and updated, SMC reset, NVRAM reset (caused boot loop afterwards), Safe Mode has no effect on fan or kernel task. It appears that there is a hardware malfunction going on inside for sure. My question here is what hardware would you suggest being the culprit? All functions seem to work without an issue (i.e. Sound, WiFi, Bluetooth, etc). Most of the issues through web searches deal with laptops with the PFM006 error from liquid damage through the trackpad. I’ll be opening it up this week once the screen tape kit comes in and I’m going to clean fans and probably replace the HDD with an SSD while I’m in there (from other forums this model does not have a separate HDD temp sensor, maybe the HDD that is installed is having issues with its internal sensor?) Any one have a similar issue that might have some insight as to what else to check?
First I would hold off replacing the HDD for now. As you have a deeper issue than a bad drive. I would double check what this system was originally configured to see if it was altered (upgraded). I’m thinking someone damaged the logic board when they added a blade SSD. The other possibility is a power surge damaged something. You’ll likely need top pull the logic board to make a proper inspection making sure you don’t see any burnt chips or missing SMT components (those very tiny resistors, capacitors, or coil components). You might want to ask your friend a bit more of this systems history maybe he can give you a clue or two. Let us know what you discover!
