System Overview

System overview

Control module





The primary task of the headlamp control module (HCM) is to manage the functions of:
- Automatic headlamp levelling (vehicles with Bi-Xenon lamps)
- Active headlamps (vehicles with active headlamps only)
The control module is mounted on a bracket toward the cowl panel in the cold zone between the engine compartment and passenger compartment. The entire control module is removed from the vehicle upon replacement.
The headlight control module (HCM) communicates both with directly connected components, and with other control modules via CAN communication.
The control module checks activations and input and output signals using an integrated diagnostic system A diagnostic trouble code is generated if the control module detects a fault. In certain cases the control module replaces the faulty signal with a substitute value.
Any diagnostic trouble codes are stored in the relevant control module memory. The data can be read off using a diagnostic tool.
A diagnostic trouble code (DTC) is registered in the internal memory of the control module if it detects a fault. At the same time, a number of values are stored. These are frozen at the time the fault occurred. Depending on the severity of the fault, certain functions may be partially or completely disengaged. A warning lamp lights in the driver information module (DIM) to inform the driver that a fault has occurred. A warning or information text will also be shown in the text display on the Driver information module (DIM).
The text shown depends on the fault. Diagnostic trouble codes and frozen values (extended fault code information) can be read out using the diagnostic tool via the data link connector (DLC) in the vehicle.
Ignition switch position II can be activated to check that the headlamp control module (HCM) is supplied power and is grounded. If the headlamps make a reference sweep, the headlamp control module (HCM) is receiving power.
For further information, also see Signal specifications.

Signals
The table below summarizes the input signals to and output signals from the headlamp control module (HCM). The signal types are divided into directly connected signals, serial communication and CAN communication. The illustration below displays the same information with the Volvo component designations.