Chosen Solution
Basically what the title says. Macbook was running super slow and fans full blast. Apple diagnostics came back with bad SMC and power management system (PFM006 and PPN001). So I replaced the logic board and I’m getting the same issues. What could cause this? No water nor apparent physical damage to the Macbook.
SMC errors are common even if the board itself is not at fault. It’s much more likely to be that the SMC is not hearing from one of the many sensors throughout the computer, or one of the sensors is getting bad readings. Agree that it’s possible your battery is at fault based on the power management error. Some parts of the power management system in this model are on the battery board, which is separate from the logic board. If you’ve already gone through all the trouble of replacing the logic board, I would see what happens if you try to run diagnostics with the battery intentionally disconnected. Or at least the battery data cable. See if you get different errors. If you just get a battery not detected error in diagnostics, seems like the battery is likely to blame. You may still get SMC errors (because there will still be sensors it’s not getting expected values from), but see if it resolves the Power management one. EDIT: Battery data cable in question is circled. The big fat screw with the arrow pointing at it is for the actual power from the battery coming into the board. All the little cable does is report things like presence, charge levels, temp, etc….
Turned out to be the top case somehow. The battery looked fine in CoconutBattery but the machine ran glacially slow–took like half a day to finally log in and get CoconutBattery to run (not even exaggerating, sadly). Replaced the top case, and with the original logic board, battery, and screen, it runs like a top. Who knew?
Diagnostics is a bit tricky! You’ll often get a SMC error, but no because of its failure only the fact the signal it’s expecting failed from upstream. Here it’s likely your battery voltage sensor. Download this gem of an app CoconutBattery post a snapshot of the main window with battery tab exposed so we can check things out.
