Active Valve Control System
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.
AVCS is used on the Version 7 and up EJ207 engines, the EJ255 and EJ257, the second generation EZ30D (2005+ in the USA Market) found in the Legacy Outback, Legacy 3.0R and the B9 Tribeca. A Dual AVCS system utilizes both the intake and exhaust camshafts on the EZ36 found in the 2008 Tribeca. Dual AVCS is also found on Japanese Spec engines, although a complete list of the engines with Dual AVCS has yet to be compiled.