Glow Plug Control Units regulate current delivery to diesel engine glow plugs during cold starts and initial operation. Typically located within the engine compartment near the intake manifold, these units utilize solid-state switching to precisely control glow plug heating duration and intensity. Internal temperature sensors and engine coolant temperature data inform the control unit’s algorithms, optimizing glow plug activation for reduced emissions and improved cold-start performance. Modern units often incorporate diagnostic capabilities, reporting glow plug failures or circuit anomalies via the vehicle’s CAN bus. Pulse-Width Modulation (PWM) is a common method employed for fine-grained control of glow plug heating.