Hi,
I have experience with ESP8266 which is close enough to ESP32, and creating APIs, mainly Java and Javascript. This project is very interesting for me, because most of IoT related projects I have done before are mainly for home automation. Interfacing Car through ODB, a novelty for me, and I would be glad to do it.
Firstly, I would implement the ESP32 to API interface for exchanging commands and data.
Secondly, I would work getting the data from the ODB and posting it through to the API.
Lastly, I would work on sending commands to the ODB.
Probably an API is not the best solution for this project, maybe a Websocket interface is better. We could try out both.
If you would like to discuss ideas around the project just drop me a message on the chat.
Regards
Juan Labrada