Diesel Glow Plug by Bosch®. Bosch Glow Plugs are critical for starting up a diesel engine. The pre-heat, starting and post-glow phases of a glow plug’s operation affect not only the start-up function, but the vehicle’s overall performance as well. With a long history of diesel fuel injection expertise and innovation, Bosch engineers manufacture glow plugs to withstand the rigorous demands of today’s diesel engines.