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.
Control Module
The primary task of the headlamp control module (HCM) is to manage the functions of:
- Automatic headlamp leveling (vehicles with Bi-Xenon lamps)
- Active headlamps (vehicles with active headlamps only)
The control module is installed on a console on the left fender liner. When replacing, remove the whole control module from the vehicle.
Headlamp Control Module (HCM) communicates both with directly connected components, and with other control modules via CAN-communication and LIN-communication.
The control module checks its calculations all performed activations as well as input and output signals with integrated diagnosis. When the control module detects a problem, a diagnostic trouble code is generated.
Any diagnostic trouble codes are stored in the relevant control module memory. The data can be read off using a diagnostic tool.
If the control module detects a problem, a diagnostic trouble code is registered in the control module's internal memory. At the same time, a number of frozen values stored from the time when the problem occurred.
Depending on how serious the problem is, certain functions will be completely or partly disconnected. A warnings or information text will be shown in the text display in the Driver information module (DIM).
If the vehicle is equipped with active headlights and these are activated (light switch in position "3"), the diode in Light switch module (LSM) will flash.
Diagnostic trouble codes (DTCs) and frozen values (extended fault code information) can be read off using the diagnostic tool via the data link connector (DLC) in the vehicle.
Ignition switch position II must be activated to check that the headlamp control module (HCM) is supplied power and is grounded. If the headlights make a reference sweep, the headlamp control module (HCM) is receiving power.
For further information, see SIGNALS .
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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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