Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Left headlight control unit (LHCU) / right headlight control unit (RHCU)
The left headlight control unit (LHCU) / right headlight control unit (RHCU) are located within the headlights.
The left headlight control unit (LHCU) / right headlight control unit (RHCU) handle the active regulation of the light beam. Active regulation means that the light beam is turned out to the left or right. The light beam is turned out at different amounts and different rates depending on vehicle speed and steering wheel angle.
Information is transferred between the left headlight control unit (LHCU), right headlight control unit (RHCU) and headlight control module (HCM) via LIN communication.
The lamp housing contains a sensor that indicates whether the light beam has been turned out to the right or left. The left headlight control unit (LHCU) and right headlight control unit (RHCU) send this information to the headlight control module (HCM).
If there is no communication with the headlight control module (HCM) or a fault arises in the left headlight control unit and/or the right headlight control unit (RHCU), active regulation ceases. If this is the case, the headlights are aimed straight ahead.
The left headlight control unit (LHCU) and right headlight control unit (RHCU) can be diagnosed.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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