Panasonic KX-T336 System Reference Manual page 1354

Testing sequence after dialing "90" is given below by using an example of PITS model
KX-T123230.
In LED test, " " means the light off, "
means flashing.
LED test
1) Testing the DN button indicators and the ICM button
indicator for lighting in green.
Panasonic
LED
EASA - PHONE
2) Testing the DN button indicators and the ICM button
indicator for flashing in green.
Panasonic
LED
EASA - PHONE
12-C-27
(70695)
" means the light on, "
TEST
DN buttons
ICM button
TEST
DN buttons
ICM button
"