Every new car today comes with ODB2 – a federally mandated on board diagnostics computer which is used for service related matters. OBD2-equipped cars have a distinctive port hidden somewhere in the passenger compartment, into which a diagnostic device is connected. When your car is running rough or the check engine light is illuminated, a ‘scan tool’ is often the first tool deployed to isolate the issue. While many auto parts stores will perform a scan for you either for free or for a nominal fee, nothing beats the convenience of having your own scan tool. Here are the best ODBII scanners to keep handy in case things ever go wrong.