CSS Electronics - J1939 DBC File - Decode Heavy Duty Data [PGN & SPN Database]

Outline

What is a J1939 DBC file?

What is a DBC file?

A DBC file is a standardized method for storing the "rules" on how to interpret raw CAN bus data. In particular, it contains details on what 'signals' (e.g. RPM, Vehicle Speed, …) are contained within which 'messages' (i.e. CAN IDs).

In the J1939 standard, messages are referred to as Parameter Group Numbers (PGN) and signals as Suspect Parameter Numbers (SPN).

Further, a DBC file includes names, descriptions, positions and lengths of the signals - as well as how to offset & scale them.

This DBC file download includes:

• An SAE J1939 DBC file with ~1800+ PGNs and 12000+ SPNs
• The J1939 Digital Annex Excel file (with additional PGNs/SPNs and description details)
• One legal license (1 user, 1 PC) matching the DA license (stand-alone price: 250$)

CSS Electronics acts as a re-seller for the Society of Automotive Engineers (SAE) for the J1939 database file. Terms include the SAE terms related to purchase.

When is the database useful?

The J1939 protocol is used across most heavy-duty vehicles, including commercial trucks, tractors, transit buses etc. Because the protocol is standardized, you can use the J1939 DBC file to decode data across the majority of heavy-duty vehicle brands/models.

For basics on J1939 data logging, see our J1939 telematics intro.

Will the DBC decode all J1939 SPN signals?

In our experience, the DBC typically lets you decode 60-80% of the J1939 signals (SPN) from a J1939-based heavy duty vehicle, with the rest being proprietary OEM-specific data. In most cases, this lets you extract the most critical signals, e.g. information related to speed, rpm, fuel data, temperatures, pressure data, GPS (if the vehicle supports it) etc. With that said it depends a lot vehicle-by-vehicle, so we always recommend to perform tests for the specific heavy-duty vehicles you need to record J1939 data from.

Can I test what data the DBC will decode?

If you're using our CAN loggers, we can offer to decode a sample log file with the DBC before you decide whether to purchase the J1939 DBC file (this sample conversion is 100% free). This way you can see exactly what data parameters you can extract from a specific vehicle (or multiple vehicles) before deciding. Simply contact us with your data samples.

If you do not have one of our CAN bus data loggers, you can perform an evaluation by parsing the unique CAN IDs from your application (e.g. logged with another logger) into our CAN ID to PGN converter to check which of your CAN IDs are matched by the DBC file.

What PGNs are in the DBC?

If you have a list of CAN IDs from a J1939-based vehicle, you can paste them in our 'CAN ID to J1939 PGN converter':

• Convert raw CAN IDs to PGNs
• Convert PGNs to raw CAN IDs
• Check if the PGNs are in the DBC

Try sample data & DBC

Below you'll find a J1939 data log from a truck recorded with the CANedge2. The sample also contains a demo J1939 DBC with EngineSpeed + WheelBasedVehicleSpeed.

You can load the raw data & DBC in the free asammdf GUI, decode it to human-readable form and plot it.