What are VANOS Solenoids on a BMW? 

The solenoid is a small component that pushes oil through the VANOS system, it makes changes as oil pressure changes. So, VANOS is a variable valve timing system used by BMW on petrol engines since 1992 to enhance the efficiency of BMW intake performance. The VANOS system varies the timing of the valves by moving the position of the camshafts in relation to the drive gear and the relative timing between inlet and exhaust valves is changed.