First need to make a battery temporary jig using the CBT156 empty battery case supplied with the radio. See picture in the bottom of this modification.
Insert CBT156 into C156E.
Press Function & Monitor butoon whilst turning the radio on.
Type 278B on keypad
Turn rotay switch until display shows "11. Tx Wide Prohibit"
Hold Function button and turn rotary switch to change "Prohibit" to "Permit"