You are supposed to do it through iTunes. Click on the iPod when you have it plugged in, and then check "Enable Disk Mode." After this, you should see it show up in Finder.
If you have an older iPod model without a Click Wheel
Before placing the iPod into disk mode you should verify that it has a charge.
Toggle the Hold switch on and off. (Set it to Hold, then turn it off again.)
Press and hold the Play/Pause and Menu buttons until the Apple/iPod logo appears, then release them. This resets iPod. When you reset iPod all your music and data files are saved, but some customized settings may be lost.
When the Apple logo appears, immediately press and hold the Previous and Next buttons until the Disk Mode screen appears.
Connect the iPod to your computer; the screen on the iPod will change and say "Do not disconnect"
To return it to its normal operating state, you will have to reset iPod.
Yes i know that, thanks for that. But apple does not give instructions on how to get into the diagnostics. At least i dont think so. They act like its not even there.