Abnormal (Hardware-) Problem with the iMac 5K 27“ - 2017

I probably need a top specialist for the following problems

What happened

While I was writing an email, the fan started up to maximum speed, the system reacts with a delay. (Process kernel_task> 300%)

What didn't help


What does Apple Diagnostics mean

Last Run: 14/02/2021, 11:19 am

Version: 1.1.38v4

Reference Code (s): PFM006

Apple Hotline recommended a visit to the Apple Service Provider - when I arrived, my iMac was analyzed, with the result that no errors were detected - the iMac behaved completely normally, which I was able to confirm later at home.

I run an Apple diagnosis again - result = no error

see query in the terminal:

sudo powermetrics --samplers smc

**** SMC sensors ****

CPU Thermal level: 0

GPU Thermal level: 0

IO Thermal level: 0

Fan: 1202 rpm

CPU the temperature: 49.02 C

GPU the temperature: 40.00 C

CPU limit: 0.00

GPU Plimit (Int): 0.00

GPU2 Plimit (Ext1): 0.00

Two days later, 1 second after switching on, the fan immediately goes to full speed, the system reacts again with a delay. The delay can be explained because in this state the CPU + GPU are clocked down (Plimit)

see query in the terminal:

sudo powermetrics --samplers smc

**** SMC sensors ****

CPU Thermal level: 255

GPU Thermal level: 255

IO Thermal level: 100

Fan: 3592 rpm

CPU the temperature: 36.22 C

GPU the temperature: 36.00 C

CPU limit: 33.00

GPU Plimit (Int): 3 p.m.

GPU2 Plimit (Ext1): 19.00

And this has been going on for a few weeks, a few days it's going well, a few days it's going bad.

The SMC values ​​that can be read out using the HWSensors tool are also interesting:

some of these SMC values, which supposedly have something to do with the power supply, show this state:

Tp2F () - 35, 35

Tp2H () - 128, 128 ——————> (what does that mean, value not available?)

Tp2h () - 31.9375, 31.9375

…. if it goes well, then there are these values:

Tp2F () - 32.6328, 32.6328

Tp2H () - 32.5, 32.5

Tp2h () - 32.5, 32.5

My question now is, what is going on with my iMac, what is broken, the logic board or the power supply - has anyone experienced this condition before?

I would be happy to hear from you.

Diese Frage beantworten Ich habe das gleiche Problem

Ist dies eine gute Frage?

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Has the system been serviced or enhanced? If so what was done.


Nothing on the system has been expanded or modified and has been in the same place for 3 years.


Now the imac has been running for 3 days without any problems.

How can that be?


@pietpiet - You might want to check your AC power service. Check the outlet to make sure it's properly wired and grounded. Lots of strange problems can be due to low voltage or bad wiring/ground.


PFM006 error which is a thermal sensor error. What is basically happening is that kernel is stuck starting and stopping computer intermittently to allow it to cool. So it hogs all cpu resources.


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