How will CarMD help me in my search for a used car? Most people have a trusted mechanic check out a used car before buying. But the process of working with the seller and your mechanic to schedule an appointment can be a hassle. We know your time is valuable. Whether you’re visiting a used car dealership or private party, don’t forget your CarMD tester. Having CarMD with you in your used car search is like having a mechanic’s second opinion in your pocket. The CarMD tester has easy-to-read LEDs that will give you a quick indication of whether or not the used car you’re looking at is a lemon – even if you can’t get to a computer for a full diagnostic report. Use CarMD before your test drive to check out the vehicle’s on-board computer – the part you can’t see with a visual inspection. Just plug your CarMD tester into the vehicle’s OBD2 port, turn the ignition to ON and wait for the beep. Once CarMD testing is successfully completed, it will display a red, yellow or green LED to give you a quick indication of possible problems.