All these codes are collected from different sources in the internet. I have tested only some of them. Some of these may not work on all models. So, please try at your own risk.
Test mode : 2945#*#
Secret menu : 2945*#01*#
IMEI no: : *#06#
IMEI & SW : *#07#
Software version : *8375#
Recount checksum : *6861#
Factory test : #PWR 668
Simlock menu : 1945#*5101#
Simlock menu : 2945#*5101#
Simlock menu : 2945#*70001#
Simlock menu : 2947#*
LG-U81XX SPECIAL CODES
Code to read phone version without SIM : 277634#*# or 47328545454#
Code to reset phone without SIM : 277634#*# or 47328545454#
Code to enter UNLOCK MENU wit SIM : 2945#*88110#
Test Menu 8330 : 637664#*#
Test Menu 8180 V10a : 49857465454#
Test Menu 8180 V11a : 492662464663#
Test Menu 8130-8138 : 47328545454#
Test Menu 8110-8120 : 277634#*#