[HID Headlight adjuster] How does it work?

As the title says: how does the ECU control headlight aim anyway? I've started having the red "triangle of death" and headlight warning light show up from time to time and have read some sensor repair threads, but nowhere have I seen it discussed the mechanism by which lights are raised/lowered. Is it done electronically somehow; small stepper motor, etc.???

The little cast actuation arm has been broken on my car for quite some time but the arm on the sensor still moves. I'm assuming the warning light comes on because the voltage seen by the ECU is outside of nominal values?

TIA