Oilyman

In case of a fault related to VANOS/Camshafts. Few known causes can be checked:

Dirty or faulty VANOS Solenoids: The most common cause, where the exhaust solenoid sticks, jams, or fails completely.
Dirty oil/Low Oil Pressure: Old or incorrect oil affects solenoid operation. The oil being a hydraulic medium for the VANOS must always be clean and compliant
Camshaft Position Sensors: Faulty sensors causing incorrect timing readings. They get demagnetized with age or coated with metal/gunk debris
VANOS Check Valves: Clogged non-return valves in the engine block. Especially the exhaust one.
Camshaft Ledges or Adjuster: Worn camshaft bearing ledges (especially on early N52s prior to 2008) or worn adjuster gears.

FCP Euro has a good article on the camshaft bearing ledge issue on high mileage or poorly maintained N52 engines.

Range	Description
0° to +-2°	Excellent
+-2° to +-5°	Normal
+-5° to +-8°	Acceptable
+-8° to +-10°	Borderline (Mechanical or hydraulic issue)
out of +-10°	Mechanical timing/reference fault

Positive adaptations

Negative adaptations

Vanos actuator reacts more aggressively than expected (e.g. Higher oil pressure due oil galleries slightly clogged or wrong oil specs)
Tuning. Default adaptations set on DME in the case of a detuned version
Camshaft installed advanced to nominal angle
One or more cylinders suffer from mechanical issues (e.g internal leak). DME pulls timing in the form of permanent negative adaptations in order to prevent mis-ignition damage
Aging camshaft sensors over-reporting the correct camshaft position