Like in a previous post I stated I recently replaced my stock headunit with a Pioneer AVH-X3600bhs - Which I got from Crutchfield on a great deal including all installation parts and adapters. I also purchased the Iphone Video adapter which works with this headunit via A app called "App-radio" you can use certain apps from your phone right on the headunits nearly 7" display. When I first read about it I was skeptical how well it would work but it works like a dream. My now non navigational heanunit has been turned into a GPS by Iphone and apps like "Waze". But the one app that really sealed the deal for me is called Dash Command.
You use it in conjunction with a wifi or Bluetooth(depending on Android vs ios) OBD2 scanner which you can get the ELM327 off ebay for under $20. I opted to go with a slightly more expensive scanner form Vgate which cost $30 for the better reputation, actual facts about the product, and software it used. Then I downloaded Dash Command for $9 and the PIDs for GM for another $9. So all in all $50 for the scanner and software but like i said could be done cheaper using cheaper components and software. This was just my choice.
I can now read live data from my OBD2 port right to my radios headunit (while still streaming bluetooth from the iphone to the headunit) Its an awesome tool and resource to have and the Fuel Mileage Calculations are priceless and so is the data logging. Here is a video I did not make it just using it as a example. https://www.youtube.com/watch?v=7DIh4u0bAgY