Structure and function of 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.
Important safety note
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.
|88 x 130 x 25 mm (L x W x H)
|Operating temperature range
|-40°C to 105°C
|3 - 8
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.
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.
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.
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.
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.
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:
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.
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.
For example, some light functions can consequently be adapted to the respective country-specific requirements.
Switch-on conditions for daytime running light
Programming modifies the existing software. This rewrites the control unit’s basic operating program.
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.
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.
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!
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