Remote Ignition Block is an OnStar feature that prevents the engine of an automobile reported as stolen from starting.
Part of the OnStar Stolen Vehicle Assistance feature set, Ignition Block works by sending a remote signal to the vehicle using the OnStar system. The service is performed by OnStar sending the ignition block signal to the vehicle, which typically requires that a vehicle be reported as stolen to the police.
To note, Ignition Block does not shut down the engine of a vehicle. Instead, it prevents it from starting.