To find out the Applications is in Maintenance Mode or not, run the following sql statment

SQL> SELECT FND_PROFILE.VALUE(‘APPS_MAINTENANCE_MODE’) FROM DUAL;

If it is in Maintenance Mode the above query will show as follows:

FND_PROFILE.VALUE('APPS_MAINTENANCE_MODE')
-------------------------------------------------------------------------
MAINT

If it is not in Maintenance Mode the above query will show as follows:

FND_PROFILE.VALUE('APPS_MAINTENANCE_MODE')
--------------------------------------------------------------------------
NORMAL

To enable or disable the Maintenance Mode in command level run the following statements in your sql prompt. Before running these statements source your apps environment.

Enable Maintenance Mode: SQL> @$AD_TOP/patch/115/sql/adsetmmd.sql ENABLE

Disable Maintenance Mode: SQL> @$AD_TOP/patch/115/sql/adsetmmd.sql DISABLE

-->We can also enable or disable Maintenance mode through adadmin