A range of PGNs (00FF00, inclusive) is reserved for proprietary use.
PGNs define the data which is made up of a variable number of Suspect Parameter Number (SPN) elements defined for unique data.
Although many modern engines use camshaft phasing, adjusting the lift and valve duration in a working engine is more difficult.
One driving force behind this is the increasing adoption of the engine Electronic Control Unit (ECU), which provides one method of controlling exhaust gas emissions within US and European standards.
Consequently, SAE J1939 can now be found in a range of diesel-powered applications: vehicles (on- and off-road), marine propulsion, power generation and industrial pumping.
Under J1939/11 and J1939/15, the data rate is specified as 250 kbit/s, with J1939/14 specifying 500 kbit/s.
The session and presentation layers are not part of the specification. All J1939 packets, except for the request packet, contain eight bytes of data and a standard header which contains an index called Parameter Group Number (PGN), which is embedded in the message's 29-bit identifier.