ODBII however allowed for manufacturer dependent codes. However, most of the codes the Prius puts out even for hybrid component problems are prefixed as standard ODB codes, rather than manufacturer specific.
But again, DTC is a code (it its the C in DTC) and not a device. Devices generate or read DTCs. There is a standard for DTCs as of 1996, although even that standard has deviations on how to present the DTCs. There are something like 4-6 accepted methods of transmission of data across that DLCIII, the latest being CAN.
But ODB only specifies errors and such that need to be available to a reader and technician mostly for emissions. It does not disallow additional proprietary functions that might be used to perform tests, produce operations for repair or diagnostics (such as opening/closing valves, running pumps, actively displaying switch/sensor outputs), or change settings, especially settings not related to the drive train, such as alarm settings, door lock settings, etc.
There is or was talk in congress to do more standardizations, and to have manufacturers disclose communications, so that third party tool developers could emulate those functions, as it is unfair to independent repair centers that they have to buy specialized scanners for each manufacturer or be locked out of being able to do repairs on vehicles.
At the very least, software should be obtainable at a reasonable price that can be installed on standardized PDAs and/or computers.
