J1939 set of profiles

The SAE website provides all SAE J1939 and cross-referenced SAE documents, plus a select group of related standards at www.sae.org

The SAE J1939 set of profiles is based on the Controller Area Network (CAN) data link layer (ISO 11898-1) using the extended frame format (29-bit identifier). Several documents have undergone revision after the initial publication in 1998. The specifications have been added to, parts taken off and clarified. The set of specifications, available from SAE, includes:

  • J1939/11 Physical layer (250 kbit/s, twisted shielded pair)
  • J1939/13 Off-board diagnostic connector
  • J1939/15 Reduced physical layer (250 kbit/s, unshielded twisted pair)
  • J1939/21 Data link layer
  • J1939/31 Network layer
  • J1939/71 Vehicle application layer
  • J1939/73 Application layer diagnostics
  • J1939/74 (Draft) Application - Configurable messaging
  • J1939/75 Application layer - Generator sets and industrial
  • J1939/81 Network management

The naming of the layers is not always compliant to the OSI reference model and to CiA's recommended terminology. The J1939/21 and J1939/31 define partly an application layer, and the J1939/71 and J1939/73 specify an application profile.

SAE J1939/11

This physical layer specification is based on the ISO 11898-2 standard (CAN high-speed physical layer). It defines a single, linear, shielded twisted-pair of wires running around the vehicle linking each of its ECUs together (3-wire connection: CAN_HI, CAN_LO, Shield). The topology is defined as a linear bus with a bus speed of 250 kbit/s and termination resistors to reduce reflections. A J1939 network can be made of multiple bus sections, each one linked with a bridge. The main function of the bridge is to provide electrical isolation between different segments so that electrical failure of one system will not cause such failure to an adjacent system. For example, the failure of the CAN/J1939 system on the trailer should not cause the failure of the truck's tractor main CAN/J1939 control system. The maximum number of ECUs is 30, and the maximum bus length is 40 m.

SAE J1939/13

This specification defines a standard diagnostic interface to a diagnostic tool in the driver's cab.

SAE J1939/15

As described in the SAE J1939 document, there is a minimum of seven documents required to fully define an SAE J1939 network. This document, SAE J1939-15, describes a physical layer utilizing Unshielded Twisted Pair (UTP) cable.

SAE J1939/21

This document is the heart of the specifications. It describes commonly used messages such as Request, Acknowledgement, and Transport Protocol. The Transport Protocol specifies the breaking up of large amounts of data into multiple CAN-sized frames, along with adequate communication and timing to support effective frame transmission between nodes. Slight modifications have added flexibility to the Transport Protocol, allowing the sender (server) of data to specify the number of CAN frames to be sent at any one time. Previously, this number was greatly determined by the receiver's (client's) limitations in the number of frames it could receive.

The 29-bit identifier comprises the following sub-fields: priority (3 bits), extended data page (EDP, 1 bit), data page (DP, 1 bit), PDU format (PF, 8 bits), PDU specific (PS, 8 bits), and source address (SA, 8 bits). The source address field ensures unique CAN identifiers, so no two nodes can ever transmit the same CAN identifier.

In the beginning, J1939 grouped several parameters (signals) together into a Parameter Group (PG). Each PG was then assigned a Parameter Group Number - its PGN. The PGN identifier contains the EDP, DP PF and PS fields. This structure has since caused some confusion with regard to PDU1-type (destination-specific) messages. Since the PDU-specific (group extension) field becomes the Destination Address in a PDU1 message, the question arose if the PGN changes, which is does not. The PGN is a static number referring to the data being transmitted and should be considered independently of the CAN identifier.

SAE J1939/31

This specification describes repeaters, routers, gateways, and bridges. The bridge functionality, how CAN messages from one network to an another are transferred, employs a message filter function to reduce the transmission of CAN messages in the individual network segments.

SAE J1939/71

In the application profile all parameters as well as assembled messages called parameter groups are specified. Each CAN message is referenced by a unique number, the PGN. The latest release of the J1939/71 document incorporates several approved additions, and brings the total number of defined messages up to almost 150. New message additions support anti-theft, fuel-specific, turbocharger, ignition, and tire pressure functions, among others. These additions and enhancements include the addition of the "source address of controlling device" parameter to several engine, transmission and brake controller messages. Inclusion of this parameter in a message will allow the receiving device to identify the original source of the message (e.g., a particular device from a bridged network). PGs are added quarterly to the document.

SAE J1939/73

Additions to the diagnostics document (J1939/73) involve memory access, start/stop functions, binary data transfer, security, and calibration information. Memory access is provided with security levels. The start/stop message is used during diagnostics performance, to quiet other devices (including nodes providing bridges to other networks). Revisions of the J1939/73 document also provide clarification regarding DTC (diagnostic trouble code) encoding in the data field. This encoding, previously interpreted differently by various manufacturers, was standardized, utilizing the reserved bit as the Conversion Method (CM) bit.

SAE J1939/74

This particular document, SAE J1939-74, describes the message structure for a set of messages which enable the user to determine and announce to others on the network, the parameter placement within a particular message from the special set of messages defined within this document.

SAE J1939/75

This particular document, SAE J1939-75, describes the parameters and parameter groups that are predominantly associated with monitoring and control generators and driven equipment in electric power generation and industrial applications. Parameters and parameter groups that may be associated with monitoring and control of the power units, such as engines, turbines, etc, that power the generators and driven industrial equipment and which may be applied in on- and off-highway applications, shall be documented in SAE J1939-71.

SAE J1939/81

The J1939/81 Draft includes state diagrams for initialization and more clearly defines constraints on the use of addresses. Its main function is to define address claiming that will ensure unique source addresses on the network.

Other SAE J1939 specifications

The J1939/82 Draft specifies the proper procedure for self-compliance and presents a scripting language that tightly defines compliance processes, and the J1939/83 Tutorial Draft provides an explanation of J1939.

For more detailed information please visit www.sae.org