OBD stands for "On-Board Diagnostics", a computer-based system built into modern vehicles. OBD monitors the performance of some of the engines' major components, including individual emission controls. The OBD system on a vehicle normally consists of one or more ECUs (Electronic Control Unit - basically a computer), a Malfunction Indicator Light (MIL), Diagnostic Link Connector (DLC), and the wiring that connect these different elements. The system provides owners with an early warning of malfunctions by way of a dashboard "Check Engine" light (also known as a Malfunction Indicator Light or MIL, for short). By giving vehicle owners this early warning, OBD protects not only the environment but also consumers, identifying minor problems before they become major repair bills.