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Wes, Consultant
Category: Mac
Satisfied Customers: 962
Experience:  Bachelor's Degree in Computer Science, 20+ years experience.
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Have an iMac with OS X software. Apple hardware test

Customer Question

Have an iMac with OS X software. Apple hardware test detected an error 4MDT/4/400000002:CPU - 0 What is this error and what should I do to fix it?
Submitted: 1 year ago.
Category: Mac
Expert:  Wes replied 1 year ago.

is it 4MDT or 4MOT? If it's 4MOT, it's probably the CPU fan has failed. How do you fix it? Well, you would have to crack open the iMac and replace that fan (or bring it into an Apple Store for repair). In order to provide more specific information I'd need to know what model or series iMac you have.

Customer: replied 1 year ago.
thanks Wes. If it is the fan, which pretty much runs constantly, can it cause a problem if not repaired or is it, the noise, just a nuisance?
Expert:  Wes replied 1 year ago.

It could lead to components being subject to a higher thermal load than normal... whether that leads to eventual failure? Its possible... basically what will likely happen is the fan noise you are hearing is causing the fan to drop below a certain rotational speed. If it stops completely, the system will over heat and shut off. The intel CPUs in most iMacs (assuming you don't have one of the REALLY OLD Motorola CPU'ed iMacs) have a thermal diode which will shut the computer off if the CPU is overheating. Its designed to shut off before any damage occurs... however, once that happens, the system will basically be useless until that fan is rep

Expert:  Wes replied 1 year ago.

replaced because the system will keep overheating and turnig off on you.