OBD2 connector with PCB

OBD2 connector to plug your project on the communication bus of your car

This connector will allow you to get connected directly on the CAN bus of car/truck/etc. To do so, you will also needs an Arduino and a  CanDIY shield

Hack your car

Is this possible? Yes, all recent cars does bring onboard computer dealing with all the devices via the  CAN bus. This CAN bus manage the data exchange between all the various component sharing the bus. Your car dealer use the OBD2 car plug to perform diagnostics, parameter tuning.
Each car manufacturer hides some secrets / keys in their update protocoles or writing specific parameters, however, the exchange protocol has been standardized so lots of informations are availables if you can access the bus (motor speed, temperature, etc, etc). With such information you can design interactive dashboard based on LDC, TFT, or even change a neopixel ribon color depending on the motor's RPM. Such informations can also be used to compute smart meter. 

Warning: don't expect to change car parameter by yourself (if you have access to confidential documents, please remember that you are doing changes at your own risks!). If you are willing to do data-logging, information tracking, smart-display, warning, all informations distributed on the CAN bus are also available to your project.