What are the best practices for using the SAE J1939 protocol in Fleet Operations?

1 Understand the protocol structure

The SAE J1939 protocol is based on the CAN bus, which is a high-speed network that connects multiple devices on a vehicle. The protocol defines how the messages are formatted, transmitted, and interpreted by the devices. Each message consists of an identifier, a data length, and a data field. The identifier indicates the priority, the source address, and the parameter group number (PGN) of the message. The PGN specifies the function and the data elements of the message. The data field contains the actual values of the data elements, which are encoded according to the parameter scaling and offset (SPN) rules.

2 Use the right tools and equipment

To effectively use the SAE J1939 protocol in fleet operations, you must have the correct tools and equipment. This includes a J1939-compliant connector or adapter that plugs into the vehicle's diagnostic port, a J1939-compliant cable or wireless interface to connect to your computer or device, a J1939-compliant software or application to view, log, decode, and simulate messages on the CAN bus (e.g. CANalyzer, Vehicle Spy, and J1939 Monitor), and a J1939-compliant database or file with definitions and descriptions of PGNs, SPNs, and data elements (e.g. J1939DA, J1939DB, and J1939DF).

3 Follow the protocol rules and conventions

In order to use the SAE J1939 protocol in fleet operations, it is essential to follow the protocol rules and conventions that guarantee compatibility and interoperability of devices and messages on the CAN bus. For instance, you must use the correct source address for each device on the bus, ranging from 0 to 253. Some are reserved for specific functions, such as engine, transmission, and brakes, while others can be assigned by the manufacturer or user. You can use a tool like J1939 Address Claiming to manage the source addresses. Additionally, you need to use the correct PGNs and SPNs for each message on the bus, which are standardized by SAE and represent common parameters and functions of vehicles. A tool like J1939 PGN Decoder can help you find these. Finally, you must also use the correct data rate and length for each message on the bus. The SAE J1939 protocol specifies a data rate of 250 kbps and a data length of 8 bytes for most messages; however, some may require a different data rate or length. You can use a tool like J1939 Data Rate Calculator to identify these values. Following these rules and conventions will enable successful implementation of the SAE J1939 protocol in your fleet operations.

4 Optimize the protocol performance and efficiency

To use the SAE J1939 protocol in your fleet operations, you need to optimize the protocol performance and efficiency to ensure the reliability and accuracy of the data and the functionality of the devices. To do this, you should use the appropriate message priority for each message on the bus, ranging from 0 to 7 with lower numbers indicating higher importance. Additionally, you should select an appropriate frequency for each message on the bus, with higher frequencies providing more current and consistent data. Lastly, you should use message filtering for each device on the bus to select which messages to receive and process, thus reducing bandwidth and CPU usage. The filtering should be most selective for specific messages that match your device's source address or PGN, and least selective for general messages broadcast to all devices or with a high priority.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?