To use the CarMD diagnostic tool, put the batteries in, plug it into the OBD 2 port, and then turn on the ignition. There is a pause while the device reads the status of the car, and then it beeps when it has read the data. When the analysis is complete, unplug it from the car, and look at the LED lights for the diagnosis.
The LED lights on the CarMD tool are green, red and yellow. If the green light comes on, this indicates that the vehicle is in good condition and it can likely pass the emissions test. If the yellow light comes on, it means that the OBD 2 system was reset and the monitors did not go through the normal tests. It may also indicate that there is an issue, but the check engine light is not yet lit. If the red light appears, the check engine light is also likely on; this shows that the car cannot pass the emissions test, but the tool gives a list of the diagnostic trouble codes.
At this point, install the CD that came with the device, and then connect the device to a computer with a USB cord. The data begins to upload, and any information available from the scan appears on the CarMD software. At this point, view the information to determine what repairs are necessary.