There are a variety of on-board diagnostic (OBD) scanners for use. Which to buy depends on the model and year of vehicle it will be used on, as well as the type of diagnostic functions needed.
The Unites States Environmental Protection Agency (EPA) required OBD to become standardized in 1996. Vehicles 1995 and earlier use use diagnostic systems unique to their manufacturer. For example, diagnostic procedures for a 1990 Ford and a 1990 Chevy Blazer are not the same. Vehicles after 1996 use the same process and system of codes.
Vehicles predating 1996 can be placed into self-testing mode. Trouble codes are conveyed by a flashing check engine light. There are scanners available for these vehicles, but each vehicle needs its own dedicated scanner. The question here is whether or not it is worth buying a scanner at all, due to their limited use and functionality.
Most OBD-II scanners are not reverse compatible. They will not be able to read code from vehicles predating 1996. They can be widely used on makes and models after 1996, however. When comparing scanners, a potential buyer needs to assess how much they will use it. Scanners can be simple code readers, good for only retrieving active codes from the OBD-II system. More expensive scanners record and display live data from a vehicle's array of sensors.
As technology becomes more advanced and sophisticated, OBD scanners become more complicated. Some scanners can be programmed to interact with other diagnostic systems, like anti-lock braking systems brakes. There are also other devices called micro-tuners. Not only can these read code and monitor sensor data, but they can be used to reprogram your vehicle's powertrain control module.
Make a list of everything needed. Consider the following questions: How many cars will it be used on? Will it be used for more than just OBD coding? Will it be needed to monitor sensors? This list can be used as a reference point while shopping online or in an auto parts store.
