Panasonic KX-T336 System Reference Manual page 503

2) After the diagnosis ends, "COMPLETE" appears and waits for
the entry of the next command.
+-- KEY test start
m Complete
Displayed Message
Displayed Message Meaning
W- Error: Illegal main command There is an error in the main command.
- Error: Illegal sub command
There is an error in the sub command.
13-D-9