Left Headlamp Control Unit (LHCU)/Right Headlamp Control Unit (RHCU) (Vehicles With Active Headlamps Only)

Fig 1: Identifying Left Headlamp Control Unit (LHCU) & Right Headlamp Control Unit (RHCU) (Vehicles With Active Headlamps Only)

Courtesy of VOLVO CARS CORPORATION

A control module is mounted under each light housing on vehicles with active headlights.

Headlamp Control Module (HCM) handles light beam control and active control of the light pattern using Left headlamp control unit (LHCU) and Right headlamp control unit (RHCU). Active control means that the light pattern is turned out to the left or right. Depending on the vehicle's speed and steering wheel angle, how fast and how much the light pattern is turned out varies.

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 a fault arises in the left headlamp control module (LHCU)and/or the right headlamp control module (RHCU), active control stops and in certain cases also the light beam length control.

Then the light pattern goes to so-called "limp home"-mode, in order to not blind on-coming traffic.

The left headlight control unit (LHCU) and right headlight control unit (RHCU) can be diagnosed.