If you want to create a mobile app to read some data from your car or any other common vehicles, you might consider to use OpenXC, which is an open API to help your development.
What is OpenXC?
OpenXC is a combination of open source hardware and software that lets you extend your vehicle with custom applications and pluggable modules. It uses standard, well-known tools to open up a wealth of data from the vehicle to developers.
OpenXC_ is an API to your car - by installing a small hardware module to read and translate metrics from a car’s internal network, the data becomes accessible from most Android applications using the OpenXC library. You can start making vehicle-aware applications that have better interfaces based on context, can minimize distraction while driving, are integrated with other connected services, and can offer you more insight into your car’s operation._
What Other Things do We Need ?
You need some hardware device to connect your mobile device and vehicle.
Plug the OpenXC vehicle interface into your car and from Android, you can read data from the vehicle in real-time like the steering wheel angle, GPS position, and vehicle speed. We are not from OpenXC, so if you want to use it, please try to get to know them more by yourself.