Electronic control units in contemporary vehicles with LED headlamps

Things you need to know and valuable tips for electronic control units in contemporary vehicles with LED headlamps.

The digitalisation of headlamp systems and their levels of technical complexity in terms of ever increasing, variable functionalities lead to increasingly higher demands for lighting electronics. A targeted control of individual LEDs enables ideal light distribution and luminous intensity, providing drivers with the best possible road visibility in every situation. Accurate control additionally avoids disturbing other, nearby road users.

Important safety note The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their work. The information provided on this website is intended for use by suitably qualified personnel only.


Structure and function of electronic control units in contemporary vehicles with LED headlamps: Design

In addition to the already familiar LED applications, such as daytime running light, position light, rear light or direction indicator light, LED technology for low beam and high beam headlamp functions have now also been established as part of exterior vehicle lighting. Additional control units are necessary to safeguard these functions.


The main objective of these light control units is to control and monitor individual light functions in the headlamp. In addition to centrally controlling all lighting functions, these control units are responsible for further coordinating activities, such as dynamically and individually adapting the light distribution of adaptive lighting systems to the respective driving situation. In vehicles with high-beam assistant, control units linked within the system control the activation of individual LEDs for each headlamp according to the situation and demand. As a result, the light intensity is controlled individually.


State-of-the-art, latest-generation LED headlamps, such as those in the VW Touareg, Audi A7 or A8, are increasingly controlled by digital systems.


Several different types of control units may be involved, depending on the vehicle and system. Control units are usually installed directly on the headlamp housing.


Arrangement of the control units (power modules) using a matrix LED headlamp as an example.


Audi A7 LED headlamp variants feature a control unit that employs a scalable concept with 4, 6 or 8 channels and has been ideally designed for controlling the various light functions in the LED headlamp. It is used to individually control the 32 LEDs of the HD matrix LED module. The control unit also generates the daytime running light signature, which is made up of twelve light segments in the A7. In this specific model, the headlamps generate a so-called light choreography once users have unlocked the doors. The animation is reversed upon once again locking the vehicle. The control unit additionally controls the swiping direction indicator. The electronic device also provides a fail safe mode. This guarantees adequate lighting even in the event of a fault.

Technical data
Dimensions88 x 130 x 25 mm (L x W x H)
Weight300 g
Operating temperature range-40°C to 105°C
LED channels8
LED outputs3 - 8 Voltage 2 - 60 V Current 100 - 1400 mA Power 40 W per channel / max. 90, 120 or 150 W
Protection classIP6K9K2
  • Matrix beam
  • High beam
  • Low beam (road surface, range)
  • (Dynamic) daytime running light
  • (Dynamic) direction indicator, see above.
  • (Dynamic) position light, see above.
  • Dynamic level control
  • Stepper motor control
Vehicle interface
  • Power supply by terminal 30
  • Ground
  • CAN bus
Special features
  • CAN communication to Body Control Module (BCM)
  • Parallel control of the LED load possible with both channels
  • Diagnostics interface including error monitoring with CAN
  • LIN communication to other control units

Light control devices on LED headlights: structure, function, diagnosis and adjustment

A little knowledge refresher: In our video crash course, we give you a general overview of the subject of light control devices on LED headlights. Find out more about structure, function and diagnostics.

LED control unit design: Design

The printed circuit board with electronic components is directly installed on the lower half of the housing. A metal housing with cooling fins is used here to ensure ideal heat dissipation.


A heat shield is additionally positioned above the printed circuit board to prevent any influence of electromagnetic or high-frequency interference on the control unit function. The metal shield absorbs interfering signals and directs them away with a corresponding ground connection. The upper housing part consists of a plastic cover that is clipped and screwed onto the lower housing part. In addition, a seal is fitted around the connector to prevent contamination or moisture between the control unit and the headlamp housing.

A further HELLA light control unit is used for LED headlamps installed in other brands’ vehicles, such as Porsche.


The following functions are provided with this control unit.


  • Power supply for low beam, high beam and daytime running lights
  • Power supply of the internal periphery with +5 V and +12 V (3 voltage converters)
  • Right/left direction identification
  • Controlling external functions (e.g. dynamic cornering light)
  • Controlling fans in the headlamp
  • Integrating up to seven signal inputs to encode temperature or light categories

Hardware architecture: Design

A control unit is required to control contemporary LED headlamps to meet the specific requirements of LED technology and the wide variety of applications.


The HELLA LMS (LED Module Headlamp) control unit has been designed to deliver maximum flexibility thanks data sets that have been adapted to the respective headlamp and installed components.


Matrix beam functionalities with dimmed transitions and animations (e.g. coming home/leaving home) can be configured with the data set, highlighting vehicle-typical identification features in the process. In addition, the control unit can be configured in graduated hardware expansion stages.


The control unit in the vehicle system is controlled by the CAN bus, providing essential inputs in addition to the actual power supply. The vehicle electric system control unit’s data input provides the device with all necessary information. Up to 8 LED channels are available at the output, all of which are dimmed by pulse-width modulation (PWM) and, in some cases, can operate several lighting functions per channel. The device additionally boasts various high-side driver outputs as well as fan control, a feature that is often required in the headlamp to reduce thermal loads. The temperatures developing on the LED printed circuit boards are detected by sensors and converted to dimming functions to protect the LEDs.


A physical CAN bus at the output connects interfaces to the widely used LED matrix managers on LED printed circuit boards. The control units also provide the LMM modules’ power supply. The device also features LIN bus outputs to provide additional communication interfaces within the headlamp.

System integration in the vehicle

In-vehicle communication with additional BUS participants is implemented by networking the headlamp control units with the vehicle electric system control unit as well as with the individual driver assistance system control units. Light control units communicate by data bus and thus receive data that is permanently and reliably converted to the required light distribution. Depending on vehicle model and system, illustrated networking overviews may differ from other vehicle models.

Testing and diagnostics: Troubleshooting

Testing and diagnostics

Superordinate control units in the vehicle electric system monitor the LED headlamp function and thus also light control units. Any occurred faults are saved in the control units’ fault memory from where they can be read out using a suitable diagnostic unit. In some vehicle models, drivers are additionally notified of system errors by a warning notice on the instrument cluster’s display.


Depending on the diagnostic unit, the following functions can be used for troubleshooting by reading out the control units as part of LED headlamp diagnosis.


  • Fault codes (reading out, evaluating and deleting fault memory entries)
  • Parameters (displaying individual measured values)
  • Actuator tests (controlling light functions with a diagnostic unit)

Carry out a visual inspection of individual system components prior to fault diagnosis with the diagnostic unit as this may help to identify and eliminate a host of faults.

Repairs and adaptation

Vehicle manufacturers are not intended to repair light control units. The control units must be replaced if the workshop diagnoses a fault in the control unit.


Potential causes of malfunctions or faults:

  • No or faulty supply voltage (+/-)
  • Internal short circuits, contact faults at terminals
  • Mechanical damage (e.g. collision)
  • Environmental influences (water, salt, etc.)


After having replaced a control unit or LED headlamp, it may be necessary to carry out an adjustment in the vehicle using the available OEM portals.


In this case and depending on the vehicle manufacturer, headlamp type and respective control unit, additional service work must be carried out with a suitable diagnostic tool to ensure the lighting system operates correctly.


The vehicle manufacturer's repair instructions refer to encoding, programming or flashing in this context. What this means in detail has been described below as part of an example, without having illustrated detailed microelectronics processes.


ESD protection must be guaranteed throughout all repair work on the LED headlamp, especially when replacing control units or other electronic components, given that electronic components, such as circuit boards or control units, may be damaged by electrostatic discharge (ESD = electrostatic discharge).


Encoding a control unit in a vehicle usually denotes the definition of certain functions that have already been stored in the software in advance.


In this process, specific lighting functions can be assigned to physical outputs or setpoints and limit values can be defined. This means that it is possible to subsequently make vehicle-specific adjustments at a later point in time. Some manufacturers also refer to this function as "variant encoding".


For example, some light functions can consequently be adapted to the respective country-specific requirements.


Switch-on conditions for daytime running light

  • Daytime running light switched on
  • Daytime running light switched off
  • Daytime running light switched on + rear light switched on


Programming modifies the existing software. This rewrites the control unit’s basic operating program. In this case, changes to the headlamp hardware, for example as part of a facelift, can be adapted on the software side.


Nowadays, an electronically programmable memory is built into every modern control unit. The components, also known as flash EEPROM, contain the control units’ operating system (firmware). This firmware can be updated to the most recent software version when installed in the vehicle. This process is also called update or flash programming.

  Since most control units require online adaptation, individual adaptation options are merged here, so that flashing has become an established and familiar term in everyday workshop life.


As part of many flash operations, programming and encoding are implemented simultaneously. Ultimately, however, the only crucial factor is that adaptation is carried out and that the lighting system in the vehicle operates smoothly.

Mercedes-Benz repair example

The right-hand LED headlamp in a W212 model series vehicle has been replaced as part of an accident repair. For this purpose, the old control units were installed on the new headlamp. After having completed the repair, a diagnostic unit was connected to adjust the QR-LED code and a macsRemote service was performed.  For commissioning, the control units of the left and right headlamps were initially programmed to a new software version and then the right-hand headlamp was encoded using the QR-LED code.


Programming, encoding or even flashing must be carried out with a suitable diagnostic unit and a stable network connection to the vehicle manufacturer's server!


Please also observe the repair and safety instructions of each individual system or vehicle manufacturer! Ensure the greatest possible levels of cleanliness when replacing electronic components in the headlamp. In addition, observe measures to protect against electrostatic discharge (ESD). Repair work on the lighting system in a vehicle must be carried out by trained specialists only. Repair work that is carried out incorrectly can lead to system failure and to severe personal injuries.

How helpful is this article for you?

Not helpful at all

Very helpful

Please tell us what you did not like.
Many thanks. But before you go.

Sign up for our free HELLA TECH WORLD newsletter to receive the latest technical videos, car repair advice, training course information, marketing campaign details and diagnostic tips.

Show additional information on our newsletter Hide additional information on our newsletter

Register for our free HELLA TECH WORLD newsletter to stay up-to-date with the latest technical videos, car repair advice, trainings, diagnostic tips and marketing campaigns.

Together we can get cars back on the road quickly!

Please note:
You will only be subscribed to the newsletter once you have clicked on the confirmation link in the notification e-mail you will receive shortly!

Data Protection | Unsubscribe

Please note:
You will only be subscribed to the newsletter once you have clicked on the confirmation link in the notification e-mail you will receive shortly!

Data Protection | Unsubscribe

Almost there!

All you need to do is confirm your sign up!
We've sent an e-mail to your email address.

Check your inbox and click on the confirmation link to start receiving HELLA TECH WORLD updates.

Wrong e-mail or no confirmation received?
Click here to enter it again.