Currently, VSS only contains support for light-duty/J2012 fault codes under the Diagnostics branch. Light-duty fault codes are currently represented as an array of strings. However, heavy-duty vehicles typically report vehicle faults via the J1939 fault protocol which uses a combination of values to describe the reported fault such as the Suspect Parameter Number (SPN), Failure Mode Identifier (FMI), Occurrence Counter (OC), and Source Address (SA). To represent these faults the VSS spec will need a more complex object type to represent the combination of these values for a single fault. https://github.com/COVESA/vehicle_signal_specification/issues/936