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 (see Fig 1) displays the same information with the Volvo component designations.

Input signals:	Output signals:
Directly connected:	Directly connected:
Position sensors (7/120-121)	Voltage feed position sensors (7/120-121)
Via serial communication:	Via serial communication:
Left headlamp control unit (LHCU) / right headlamp control unit (RHCU) (only vehicles with active headlights or GDL-lights)	Left headlamp control unit (LHCU) / right headlamp control unit (RHCU) (only vehicles with active headlights or GDL-lights)
Via Controller Area Network (CAN) communication:	Via Controller Area Network (CAN) communication:
Transmission Control Module (TCM) (4/28) Brake control module (BCM) (4/16) Steering wheel module (SWM) (3/254) Central electronic module (CEM) (4/56)	Driver information module (DIM) (5/1). Central electronic module (CEM) (4/56)

Fig 1: Identifying Headlamp Control Module (HCM) And Components

Courtesy of VOLVO CARS CORPORATION

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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System Overview: Signals

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