All OB II scanners have different specific directions, but on a basic level, they all operate by plugging them into the OBD II connector under the dash of a vehicle and turning the key, but not turning the engine. At this point, more instructions should appear on the screen of the device.
After turning the key, the tool asks for information such as the engine type, vehicle identification number, and make and model of the vehicle. Onscreen instructions may also appear, and an option may appear to check for codes. Depending on the type of scanner, there may be additional choices as well. High-end tools may give an explanation of the code on the screen, but others may require the use of a pamphlet, book or CD-ROM. The codes also might appear online by searching the Internet for the code number, make and model of the vehicle.
Another scanning option on an OB II scanner is a test for inspection and maintenance readiness. If the malfunction indicator lamp is off, drive the car until the power-train control module reads that the fault is now correct. Typically, this takes a few days of driving to reset, and the car cannot pass an inspection if the malfunction indicator lamp is on. This feature stops people from clearing the codes with the OB II scanner, then sneaking a car through inspection.