CANbus Academy

How J1939 PGN Decoding Works

In SAE J1939, every CAN message uses a 29-bit extended identifier. Unlike standard 11-bit CAN, the J1939 identifier encodes structured information about the message content, its priority, and the sending ECU.

29-Bit CAN ID Structure

The 29-bit identifier is divided into fields:

PGN Extraction from a CAN ID

The Parameter Group Number (PGN) is computed from the identifier, and how depends on the PDU type:

• PDU2 (PF ≥ 240): the PS field is a group extension, so it is part of the PGN. Example: CAN ID 0x18FF1200 has PF = 0xFF, so PGN = (DP × 65536) + (PF × 256) + PS = 65298 — a broadcast message.
• PDU1 (PF < 240): PS is the destination address, not part of the PGN. Example: CAN ID 0x0C213425 has PF = 0x21, so PGN = (DP × 65536) + (PF × 256) = 8448, addressed to destination 0x34.

CAN ID to PGN Calculator

Paste a 29-bit CAN ID and the calculator extracts the priority, data page, PDU format, PDU specific, source address, PDU class, and computed PGN. For PDU2 messages, the PS byte is part of the PGN; for PDU1 messages, PS is the destination address.

Looking for a J1939 PGN or SPN list?

The official PGN and SPN definitions are maintained in the SAE J1939 Digital Annex. This page does not include or redistribute that database. The calculator computes PGNs from CAN identifiers and can decode signal definitions from a DBC or reference file you provide.

Proprietary PGNs: manufacturer-defined messages

Not every J1939 message is defined by the standard. J1939 reserves ranges for
proprietary, manufacturer-specific data, so engine makers,
transmission suppliers, and equipment or implement manufacturers can carry whatever
the standard doesn’t cover — for example a battery-management system
(BMS), an implement controller, or a vendor-specific sensor.

• Proprietary A — PGN 61184 (0xEF00): a peer-to-peer proprietary message (the PS byte is the destination address).
• Proprietary B — PGNs 65280–65535 (0xFF00–0xFFFF): 256 broadcast proprietary messages.

Proprietary messages have no public definitions. Their bit
positions, scaling, offsets, and meaning are decided by the manufacturer and shipped
in that manufacturer’s DBC or reference file — there is no central registry
to look them up in. To decode one, load the manufacturer’s DBC into the
calculator and it decodes against those definitions.

Proprietary PGN examples (illustrative)

Payload layout is manufacturer-defined and requires the manufacturer’s DBC or reference file.

Illustrative only. “Acme Inc” is
fictional and these PGN assignments are invented to show the shape of proprietary data
— they are not real definitions. Proprietary PGNs carry no public registry; decode
them with the manufacturer’s own DBC.

Decoding signal values: bring your own DBC

The calculator decodes the structure of any J1939 message for free — priority, DP, PF, PS, source address, and the computed PGN number — with no reference data required. To decode the signal values inside the payload (the SPNs — their bit positions, scale factors, offsets, and units), load your own DBC file or reference file. The tool decodes against the definitions you supply; with nothing loaded it reports the raw decoded fields only.

Why signal definitions need an authorized source

The authoritative J1939 parameter set — the full list of PGN and SPN definitions — lives in the SAE J1939 Digital Annex, which is maintained and licensed by SAE International. If you need the official definitions, license the Digital Annex from SAE, or use a DBC file you already own. Load that file into the calculator and it decodes your traffic against those definitions, entirely in your browser.

Open the PGN Calculator and load your DBC →