Chosen Solution
I just replaced my iMac 2011 21.5 CPU fan since it was reported to have an error 4MOT/4/40000002: CPU-0 After replacing the fan, it still shows 0 speed and still is reported as the same error as above after running the Apple Hardware Test. Is there anyway I can test the fan to see if it is working on another fan connection in the iMac with the display off? Thank
Fans are very simple and they hardly go bad..if it reports the same error with two different fans it’s very unlikely they are both malfunctioning. Probably you have a problem with a resistor on the logic board causing the error.
