Since yesterday, on my iMac (A1419 EMC 2806) the fan is maxing out from power up, regardless of safe mode, recovery mode, or booting into Windows (via Boot Camp), diagnostics return PFM006 (SMC error) Assuming a thermal sensor defect, I installed iStats to check the thermal sensors. Readout below in the screenshot - all temperatures are within normal ranges, the fan is at maximum and also won't slow down if I try to do that manually, and the only temperature that's missing is the one from the power supply unit (AC/DC T2 secondary heat sink). So my question is: Is there even such a sensor in that model, do I expect a readout here? Have I thus found the probable cause and should be looking into the connection or the sensor itself? (No other hardware or software changes made recently)

Readout from iStats

  • Have you tried wether an SMC reset solves your fan issue? Does the fan spin up when booted into recovery mode? Oct 14, 2021 at 9:31
  • Yes, SMC and PRAM resets have no effect, it spins up immediately after booting and also in recovery mode. Also if I boot Windows via Boot Camp.
    – cirko
    Oct 15, 2021 at 10:25

1 Answer 1


I exchanged the power supply unit as a whole, assuming that the thermal sensor is integrated as I had read elsewhere. After that, it worked again perfectly, and also showed a normal temperature readout from the above mentioned AC/DC T2 sec. heatsink sensor.

Here's the new readout:

enter image description here

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