Reviews the emission readiness status of OBD monitors
The MaxiScan code reader supports all OBD2 protocols, including the newly released Controller Area Network (CAN) protocol. Though it is small, it is able to retrieve same information as large expensive scanners. This code reader reviews the emission readiness status of OBD monitors and determines the malfunction indicator lamp (MIL) status as well as turns off check engine light. It comes with free CD software with over 7000 DTC definitions and is powered via OBD2 cable.
Or for those that like to watch also some of the operating parameters there is a more expensive alternative the ScanGauge II:
This tool combines a scan tool and a multifunction trip computer. If you have an older vehicle that does not provide functions like current mileage, fuel consumption rate, engine speed (rpm) you can add those using this guage. (Provided your vehicle provides a compatible OBD II interface.)
Autel MaxiTrip TP100 4-In-1 Auto Computer:
It does trip computer real-time information monitoring including average trip MPG, tank MPG,
average speed, average speed per tank of gas, miles to empty, and miles driven on tank and
serves as well as a scan tool. Scan tool functionality including reading and clearing trouble
codes on OBD-II/EOBD compliant vehicles,
freeze frame data and the ability to turn off check engine light.
The reviews are somewhat mixed though.