ELM327 is a free program that allows you to use your PC and a hardware interface to get the information from your car's computer. The program is very user-friendly, and easy to learn. It is also very easy to install: simply extract the files into a folder on your computer's hard drive, and you're ready to go.
The program lets you perform the following operations:
Read diagnostic trouble codes, both generic and manufacturer-specific,
and display their meaning (over 3000 generic code definitions in the database).
Clear trouble codes and turn off the MIL ("Check Engine" light)
Display current sensor data, including: Engine RPM, Calculated Load Value,
Coolant Temperature, Fuel System Status, Vehicle Speed, Short Term Fuel Trim,
Long Term Fuel Trim, Intake Manifold Pressure, Timing Advance,
Intake Air Temperature, Air Flow Rate,Absolute Throttle Position,
Oxygen sensor voltages/associated short term fuel trims,
Fuel System status, Fuel Pressure AND Many others...