We can enable or disable maintenance mode without using adutility (adadmin), Perform the same from SQLPLUS session.

Check the current status of Maintenance Mode:

select fnd_profile.value(‘APPS_MAINTENANCE_MODE’) from dual;

MAINT     =  MAINTENANCE MODE is ENABLED
NORMAL =  MAINTENANCE MODE is DISABLED

ENABLE maintenance mode:
sqlplus -s apps/apps @$AD_TOP/patch/115/sql/adsetmmd.sql ENABLE

DISABLE maintenance mode:
sqlplus -s apps/apps @$AD_TOP/patch/115/sql/adsetmmd.sql DISABLE