Many states in the U.S. now use OBD-II testing instead of tailpipe testing in OBD-II compliant vehicles (1996 and newer). Because OBD-II stores trouble codes for emissions equipment, the scan tools can query the car's onboard computer and verify if there are emission related trouble codes if the vehicle is in compliance with emission standards for the model year it was manufactured.
In the Netherlands, vehicles made at 2006 and later get a yearly EOBD emission check.
Driver's supplementary vehicle instrumentation
It is an instrumentation installed in a vehicle in addition to that offered by the vehicle manufacturer. The instrumentation is displayed to the driver during normal operation. This is different from scanners used mainly for active fault diagnosis, tuning, or hidden data logging.
Auto enthusiasts tend to install additional gauges such as manifold vacuum, battery current etc. The OBD standard interface has made it possible for enthusiasts instrumentation accessing the full range of vehicle data used for diagnostics, and derived data such as instantaneous fuel economy.
Instrumentation usually takes the form of dedicated trip computers, carputer or interfaces to PDAs, smartphones, or a GPS navigation unit. A carputer is essentially a PC, and the same software works as well for PC-based scan tools and vice-versa. Therefore, the distinction is only in the reason for use of the software.
These enthusiast systems may also include some functionality similar to the other scan tools.