Unlike the self-controlling standard glow plugs, the new instant-start glow plugs require a voltage-controlled activation. The voltage at the glow plug is controlled by pulse wide modulation of the on-board voltage. In pulse wide mode(PWM) operation, the glow plugs are not all switched on and off simultaneously but one after another whenever possible to minimize the influence on the vehicle electrical system due to periodic switching on and off of very high currents. ISS ECU receives the current engine speed and fuel quantity per injection via the CAN bus. Based on this information, the Glow Plug Control Unit(GPCU) increases or decreases the electrical power fed to the glow plug.