[Gaffer74]

I know you can get these in various places, but every list has slighlty different menu's listed. So I thought I'd post the relevent data specifically for b&w 4th Gen iPods with Nov '05 firmware:

How to reset your iPod:
4th generation iPods and iPod mini (if you're booting from a run down battery state, plug in the power first and wait 30sec):
First click "Hold" on, then off.
Now press the "Menu" and "Select" (center) buttons together for about 5 to 10 seconds - until the Apple logo appears.
Now release. The iPod will now cycle through a soft reset.

Diagnostic Tests: If you want diagnostic tests, press the "Back" and "Select" after the Apple logo appears.
You will hear an audible chirp sound and the Apple logo should appear backwards. You are now in Diagnostic Mode.
Navigate the list of tests using "REW" and "FFW" (the scroll wheel will not function while in diagnostic mode). To initiate a test, press the Select button. To exit tests when they're completed, press the Play button.

Tests available:

5 IN 1
This runs the following 5 tests at once: Backlight, SDRAM, FLASH/CHECKSUM, RTC, and USB connection.

RESET
Resets the iPod. This is one way to exit the Diagnostic screen.

KEY
After you start this test, you need to press all the buttons on your iPod. If you don't do it fast enough it will fail (you press the keys, it tells you if they work.)

CHGR CURR
?Seems to allow you to turn on and off charging methods.

REMOTE
This will test your iPod's Remote if you have one. Plug it in or the test result will be "RMT FAIL". It now allows you to test the buttons on the remote control.

HP STATUS
Indicates if something is plugged into the headphone jack and the state of the hold switch.

SLEEP
Puts the iPod to sleep. You will need to reset your iPod to wake it back up.

BATT A2D
Checks the iPod's power supply and indicates the amount of charge in the battery.

A2D STAT
Battery and power supply statistics (inc. battery temperature).

FIREWIRE
Checks FireWire chip/port. A successful completion of the test will return "FW PASS".

HARD R/W
Read and write hard drive test. Reads HDD and gives you the disk's volume (pass if all goes well).

SMRT DAT
Another hard drive test. Mine reads RETRACTS 22 REALLOCS 1 PENDING 4.

HDD SCAN
Scans your iPod's hard drive. This is a great way to see if you have a healthy iPod. This test will take a few minutes at least so be patient & don't perform it unless the iPod is plugged into a power source.

READ SN
Displays the serial number

DISKMODE
Throws the iPod into Disk Mode.

WHEEL
Run your thumb around the wheel and watch the values change.

CONTRAST
Runs contrast test. Proceed through the screens by pressing the Play button. Press forward/backward to alter the level on each test screen. You will need to reset your iPod to exit this test.

AUDIO
Plug in headphones, you should hear some "drum beats" (this test checks the audio subsystem).

STATUS
Tells you what's plugged into your iPod -- whether it's being charged via FireWire and has something plugged into the headphone port, for example.

DRV TEMP
Displays drive temperature.

IRAM TEST
?testing the flash RAM in some way (hopefully should get "pass"). Takes a bit of time.

To get your iPod out of Diagnostic Mode, you will have to re-boot it again ("menu" and "select")

How to force mount/dismount the iPod:
Soft reset as above. When the Apple logo appears, press "Select" and "Play/Pause" together.

The iPod uses the Sony UP325385 A4H battery.