If certain keys on your VVX 400 are not responding as expected, a quick test can be run to verify the key mappings are correct and that the button itself is not broken. If no key code is returned when pressing a button, the phone likely has a hardware failure. If incorrect codes or functions are returned, the phone likely needs to be reset to factory and re-configured to reset the key mappings.
From the phone's Home screen, Navigate to the diagnostics page: Settings, Status, Diagnostics, Test Hardware, Keypad Diagnostics:
Left Line Keys (Top to Bottom)
Key 51 - Line 1
Key 32 - Line 2
Key 33 - Line 3
Key 34 - Line 4
Key 52 - Line 5
Key 53 - Line 6
Right Line Keys (Top to Bottom)
Key 54 - Line 7
Key 35 - Line 8
Key 36 - Line 9
Key 37 - Line 10
Key 55 - Line 11
Key 56 - Line 12
Softkeys (Left to Right)
Key 29 - Softkey 1
Key 28 - Softkey 2
Key 27 - Softkey 3
Key 31 - Softkey 4
Navigation Keys
Home - Key 26
Up - Key 12
Down - Key 11
Left - Key 3
Right - Key 4
Select - Key 18
Main Dialpad
1 - Key 25 - Dialpad 1
2 - Key 2 - Dialpad 2
3 - Key 5 - Dialpad 3
4 - Key 8 - Dialpad 4
5 - Key 9 - Dialpad 5
6 - Key 40 - Dialpad 6
7 - Key 15 - Dialpad 7
8 - Key 16 - Dialpad 8
9 - Key 17 - Dialpad 9
* - Key 22 - Dialpad Star
0 - Key 23 - Dialpad 0
# - Key 24 - Dialpad Pound
Left Function Keys (Top to Bottom)
Key 20 - Transfer
Key 21 - Messages
Key 19 - Hold
Right Function Keys (Top to Bottom)
Key 10 - Headset
Key 13 - Handsfree
Key 14 - Mute
HookSwitch - Key 254