4mot/4/40000003:hdd-1221 error is on iMac?

That error usually indicates a problem with the fan that cools the hard drive. You will need to take your iMac to an Apple Store or authorized Apple service center to address this problem.

Regards.

Error codes WRT to hardware are usually not available to the general public, meaning users. Contact Apple Service, iMac Service or Apple's Express Lane. Do note that if you have AppleCare's protection plan and you're within 50 miles (80 KM) of an Apple repair station, you're eligible for onsite repair since yours is a desktop machine.

Hi, I understand this to be the Hard Disk Drive fan Motor overspeed - the figure is the speed recorded with the default on my machine as 1200 rpm and the overspeed somewhere around 1320 if not working too hard (the fan should ramp up speed in any case against a calibrated speed/temperature curve, it just reports against what it is expecting, I guess) . I have had a similar issue with my iMac for over a year, if not more. As the fan is overspeed, it is just keeping the hard disk drive a bit cooler. I haven't bothered to get it fixed and don't see it as an issue. Incidently, on occasion, I have switched the machine off overnight and then done an Apple Hardware Test first thing in the morning and it has passed, and I don't lose any sleep over it.