Should the fan spin on start up or only when the component are hot?

I received these error messages after running diagnostics:

There may be an issue with the fan.

Reference Code: PPF003

There may be an issue with the Thunderbolt hardware.

Disconnect external Thunderbolt devices and run the test again. If this message appears a second time, check “Ge started below”.

My iMac was restarting randomly and the whole metal body was hot to the touch which made me conclude that the fan was indeed not working. So I purchased the required tools to open the iMac and also bought a new fan (not from here as there were not in stock at the moment). I opened the iMac and replaced the old fan with the new one.

Now before putting on back the screen I wanted to see if the fan would spin with the screen off. I plugged in the power cable and powered on the iMac the chime sound played, however, the fan didn’t spin :(.

Hence I was looking for any assistance in helping me debug my issue. I was asking does the fan spin on startup or only when components get hot?

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I would get a good thermal monitoring app like TG Pro which can allow you to visually see what your systems thermal sensors are doing as well as how the fan is responding. You can also alter the fans speed to see if it's working.


Thanks for the reply Dan. I haven't put on back the screen as indicated in the post. I don't want to put it back on and find out the fan is not working and waste my adhesive for the screen. I was considering trying to hook up an external monitor. So I'll see if this is possible.


That won't work. You need to connect the internal display as the sensors within it will mess you up.

To save you the loss of the tapes, how about using some masking tape like a good Painters tape which is strong enough to hold the display and won't damage screen.


@danj “the sensor within it will mess you up” meaning there is a sensor that detects that the display is connected and if it’s not connected then it won’t even start properly and in turn make the fan not spin. Something along the lines of that?


The system goes into hardware Safe Mode when one or more of the sensors become disconnected from SMC in this case when the display assembly is disconnected. Safe Mode pumps the fan into high RPM as well as lower the CPU's clocking to prevent the system from over heating

What you need is a an extension cable set to run the system with the display set on a frame to the side of the case. But before you go that far how about installing and running TG Pro as I had recommended at the start. Clearly you bought the needed tools to open the system, now you need to invest in the tools to diagnose your problem given what it offers for free how can you go wrong?


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