Warning: Do at your own risk. If you are not sure what it is in the hidden menu, Do not change it.
How to access the hidden menu on LG Optimus L9 II (LG D605)?
From your LG Optimus L9 II (LG D605) dialer, input the following codes, then press send:
You will be able to access the hidden menu on LG Optimus L9 II (LG D605)
You can run the full All Auto Test with the hidden menu for trouble shooting your device.
From the hidden menu, Select Device Test -> Select All Auto Test – FULL
If any of the items fail, Your device got problems, please send your device to service center to repair it.
Warning again, Do not change any option, if you do not know what it is.