On running the Apple Hardware test I get this message. The machine is a mid-2011 iMac 27" running macOS Sierra.
Alert! Apple Hardware Test has detected an error
4M0T/4/40000003: HDD-1518
The forums have similar error messages but the number after HDD is different.
Is this hard disk related or hard-disk temperature sensor related?
Thanks
iMac, Mac OS X (10.7.5)
Apple does not publish what these codes mean, your best bet is to call an Apple Authorized Service Provider and ask to be 100% sure. If you don't know of any in your area, please click https://locate.apple.com/country to begin locating one.
You can always Google the code and see what comes up too, that may help you out.
4MOT is a fan error, likely a fan which is not working or is not responding to speed commands. I would not worry about the number after the HDD. The problem can also be caused by a failing hard drive that is overheating.
No matter what the cause, your iMac needs to be looked at.
Tom
FWIW, Apple stores/Genius Bar personnel have access to far more sophisticated testing equipment, so they'd be able to diagnose it more precisely. Make sure to make a full backup (or two) before taking it in.
Apple hardware test failure message
