The active valve control system (AVCS) is an automobile variable valve timing technology used by Subaru. It varies the timing of the intake valves by using hydraulic oil pressure to rotate the camshaft in order to provide optimal air flow in and out of the engine. The system is closed loop using camshaft sensors, crankshaft sensors, air flow meter, throttle position as well as oxygen sensors and/or Air-Fuel ratio sensors in order to calculate engine load. The ECU is programmed to operate control valves that adjust the delivery of the hydraulic pressure in order to move the camshaft into the position that will provide the engine with the best performance while minding emissions standards.