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 headlamp control unit (LHCU) and right headlamp control unit (RHCU) handle headlamp levelling and active control of the light beam. Active control means that the light beam is turned out to the left or right. The light beam is turned out at varying degrees and rates depending on vehicle speed and steering angle.
Information is transferred between the left headlamp control unit (LHCU), right headlamp control unit (RHCU) and headlamp control module (HCM) via serial 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 headlamp control module (HCM) or there is a fault in the left headlamp control unit (LHCU) and/or right headlamp control unit (RHCU), headlamp levelling and active control are disabled. The light beam then assumes its "limp-home" position.
The left headlight control unit (LHCU) and right headlight control unit (RHCU) can be diagnosed.
The control units are integrated in the headlamps. If a Left headlamp control unit (LHCU) or Right headlamp control unit (RHCU) becomes damaged, the entire headlamp must be replaced.
NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
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.