A BMW VANOS uses oil pressure-powered actuators to move the camshafts. The actuators need a consistent supply of oil for the correct viscosity, pressure and volume. For some S54 engines, they use a module with valves that resemble those found in an ABS modulator. The more common design is a spool valve to control the oil on either side of the piston.
The solenoid is actuated by a pulse-width modulated signal.If the oil is contaminated or is the wrong viscosity, the VANOS system can become sluggish. If the oil pressure can’t move the camshafts to the target positions in a specified time, the camshaft position sensors will sense it and set a code.
A code will be set if the actuator and camshaft do not return to the correct position, because they are hydraulically jammed due to oil pressure leaking past a seal. When replacing a VANOS unit, make sure you are using new gasket to seal the new unit to the cylinder head.
This video is sponsored by Elring.