Today I will explain how to access information from your car on your iPhone with a "scanner" OBD-II Bluetooth like this:
This little device plugs into the socket of your car ODB II:
If you want to know what their role is, here's a Wikipedia link.
Here's what you need:
A Jailbroken iDevice (here an iPhone 4)
A Scanner OBD 2 Bluetooth (ELM327 by a home DealExtreme)
RoqyBT4 + RoqyOBD (Cydia)
An application from the AppStore to read information from the OBD for example Rev or DashCommand
1. Start by going on Cydia for download and purchase RoqyBT4 (5 €) then RoqyOBD. This tool allows you to connect any Bluetooth device (GPS, Heart, etc..) To the iPhone for compatibility with many applications.
2. Now install an OBD II diagnostic application on the appstore (DashCommand or Rev).
3. Connect the OBD II scanner to your car, then start roqyBT4. Go to Settings -> Device Selection -> generic OBD Case (works with ELM327 box). Enter the PIN code (bluetooth) of the case.
4. Return to the main page, turn on bluetooth and connect to your scanner OBD II. If the connection is successful, a message appears with the logo below:
5. The application created a local server with a bridge to the OBD II bluetooth device. It'll just run your application from the appstore and set it up:
Dashcommand -> Settings -> OBD-II data port -> Enter the information manually: 127.0.0.1 with port 35000
Dashcommand -> Settings -> OBD-II data port -> Enter the information manually: 127.0.0.1 with port 35000
Rev -> Settings -> Hardware -> Custom -> IP: 127.0.0.1 Port: 35000
6. A message tells you that you are connected to your car. Now you can read error codes and different values of your car.
Obtained from: http://iph-apps.blogspot.sg/2012/08/connect-your-iphone-to-your-car-obd-ii.html
