The stepper motor is connected to the lower edge of the pivoting reflector. The connection is through a sort of universal joint in a plastic push-rod.
The joint has neen known to get stiff enough to prevent the action. The only way to fix it or to examine the motor system is to separate the two halves of the lamp. This involves a bit of cookery in the oven at 100C. There's a HowTo on this somewhere.
Another common issue that can affect this is the headlamp harness getting chafed through where it passes over a weld seam on the body.
You need the front bumper off to get to this. It's near the screen wash bottle.
TC