Hello,
Happy to find a work on OBDII. I have a good experience in CAN communication and OBDII protocols. So far I have worked in 5-6 CAN based projects in college and in the company. In company I have worked few projects on OBD protocols SAE J1979 both on CAN and KWP2000. Also I have some experience on CANoe tool.
From your project discription I understand you are trying to use a Raspberry pi to retrieve diagnostics data. Frankly speaking I have no experience on working on a Raspberry pi. I have worked with PIC and other ARM controllers from NXP. Anyway you can't access OBDII port by only using Raspberry pi. You will need additional hardware to connect to the port. For eg. CAN controller is not available on Raspberry pi. You have to put additional controller for that. Also for other protocols on OBDII you will need additional circuits. I will need more detailed project description and the application for giving a detailed proposal and suggestions.