To provide a method for operating a glow plug to reduce the load of a vehicle electrical system.

There is provided a method for operating a glow plug with the engine running. An effective voltage is generated from a vehicle electrical system voltage by pulse width modulation. The effective voltage is applied to the glow plug and changed as a function of engine parameters. A target value of the effective voltage that is dependent on the engine parameters and to which the effective voltage is changed is predetermined. A maximum increment for a change of the actual value of the effective voltage in at least one direction is predetermined, and a change of the actual value in at least one direction to a target value that deviates from the actual value by more than the maximum increment is carried out in several steps. A controller which carries out such a method during operation is further provided.