Abstract: A method and system of power management for a vehicle communication interface that provides a connection between a diagnostic tool and the vehicle is provided. Power for the vehicle communication interface may be provided by the vehicle or the diagnostic tool depending on the configuration of the interface and tool. The vehicle communication interface can detect a presence of vehicle power and operate in full power mode when the vehicle power is available. Alternatively, the vehicle communication interface can detect the absence of vehicle power, receive power from the diagnostic tool, and start out in low power mode. The interface can then request or negotiate via USB standards for additional power from the diagnostic tool.