While the On Board Diagnostic (OBD) protocol was established by SAE in 1979, it wasn't until 1994, when California emissions regulations mandated it be included on all vehicles, that it became the industry standard now known as OBD-II.
Between 1979 and 1994, most companies used some portion of the OBD standard. Renix did not, charting their own path with a proprietary format.
While some commercially available diagnostic tools were made for mechanics, the protocol was never published. In 2012, a video by Phil Andrews of the RenixPower forum demonstrated his hard work in decoding the protocol.
Following that, Nick Grisley of NickInTimeDesign started developing the Renix Engine Monitor in 2016 and has been generous to share the source code as an open source project. There are several videos on his website that show the extensive sleuthing that was needed to arrive in his latest iteration. I've purchased one and I've been very impressed, it works great!
This project is an extension of both Phil and Nick's tremendous efforts and would not have been possible without them.