Cars rely on computers to help determine fuel delivery, ignition timing and other key functions. The Engine Control Unit (ECU) -- that’s the computer that tells the engine what to do -- uses sensors throughout the vehicle to keep a watchful eye on the health of the car. When a bad signal or code is sent to the computer it will let you know by illuminating the panic-inducing check engine light. This is where the OBD II comes in.
An OBD-II (On-Board Diagnostics) reader is an engine code reader that can talk to the ECU to determine the cause of an illuminated check engine light. Think of it as a translator for your engine's language. The tool is a valuable resource for the at-home mechanic as it reveals whether a car’s problem is something you can fix yourself or one which will require a trip to the shop.
At $100 a pop, buying one of these only makes sense if you’re convinced you can save money in the long run. Those with older or modified cars will benefit from having an OBD-II in the garage, but unless you’re a die-hard DIYer, owners with time left on their warranties have no reason to shell out for the tool.