In SAE J1939, the acronym SA stands for Source Address and represents the address of a controller application. A source address is 8-bits wide and is included in every J1939 message. Also, every J1939 controller application (i.e. ECU), has a unique SA.

J1939 requires every CA to have a unique source address (SA) to guarentee that all CAN identifiers are unique. This is a requirement of the CAN Bosch specification and is required for correct CAN functionality. J1939-81 specifies an address claim procedure which details what steps should be taken if more than one controller application (CA) has the same source address (SA).