4mot/4/40000003:hdd-1473

Along with that error code it might also be helpful to know exactly which iMac and what kind of problem you are having that caused you to run AHT in the first place. 99% of the 4mot codes I've seen have been caused by a failing hard drive.

It's a fan speed error (mot : motor)

hdd : usually means a fan close to the hard drive

1473 is the speed, in revs per minute : presumably, the test thinks it's either too high or too low.