Additional ATP Functions in Service Parts Management
If you activate the system configuration for service parts management, additional functions for availability check using SAP APO are available.
Prerequisites
In addition to SAP CRM, the following minimum system requirements apply:
SAP SCM 5.0
SAP ECC 6.0
The system configuration for service parts management is active.
You activate this configuration in Customizing under 
Customer
Relationship Management
Transactions
Basic Settings
Activate System
Configuration for Service Parts Management.
For further information on the system configuration for service parts management, see Functions in Service Parts Management.
You must carry out planning in SAP APO, planning in SAP ECC is not supported.
Features
The following functions are additionally available:
Controlling ATP Check in the Sales Order
Using these functions, you can manually control in the sales order how SAP APO carries out the availability check.