CarMD uses the On Board Diagnostics feature of cars produced the last decade to help you diagnose problems with cars.
The ODB standard defines a set of standard codes that helps identifying the problem.
It is not a replacement for a skilled technician but it can give you peace of mind:
Examine a used car before buying: The green, yellow and red lights on the CarMD tester can tell you if the used car you're considering is jewel, a possible lemon, or a big red flag.
Give your vehicle a clean bill of health before road trips : Again, watch the lights. Green = go, Yellow = proceed with caution, Red = consult your mechanic.
Pre-”smog” test your car: ...