Glow plug control units (GPCUs) manage preheating of combustion chambers in diesel engines, typically located within the engine compartment near the intake manifold or glow plugs. These units receive signals from the engine control module (ECM) regarding engine temperature and load, then regulate current to the glow plugs for optimal cold-start performance. Modern GPCUs utilize pulse-width modulation (PWM) to precisely control glow plug heat and extend lifespan, often incorporating diagnostic capabilities for fault detection. Some units feature independent circuit monitoring for each glow plug, enabling pinpoint fault identification. Advanced designs may include ceramic glow plugs and/or post-glow functionality for reduced emissions and smoother operation.