What is an ECU and what role does it play in modern vehicles?

An Electronic Control Unit (ECU) is a microprocessor-based controller that manages vehicle functions. Modern vehicles contain 30-100+ ECUs controlling engine, transmission, braking, steering, HVAC, infotainment, and safety systems. Each ECU receives sensor inputs, processes data using programmed algorithms, and controls actuators. ECUs communicate via vehicle networks to coordinate functions and enable integrated features.