In SAE J1939, the acronym PDU1 stands for Protocol Data Unit 1 and represents a message that is destination specific. If a message is a PDU1 or PDU2 format is specified by the protocol format (PF) field contained in the PGN.

A PF field less than or equal to 239 indicates a PDU1 format message. The PDU format entity was created to allow for the maximum number of PGNs but still allowing for destination specific messages.