U0241

Code

Generic U — Network/User

Lost Communication With Headlamp Control Module A

Brand: Generic

Type: U — Network/User

Views: UK: 34 EN: 72 RU: 44

AI status

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Page language: EN

Causes

Faulty Headlamp Control Module (HCM A)
Blown fuse or removed power/ignition feed to the HCM
Poor ground connection at the HCM
Damaged or corroded connector pins at the HCM
Broken, shorted or open wiring in CAN/LIN communication lines
CAN bus termination problem (open or shorted termination resistor)

Symptoms

Malfunctioning or non-operational headlamps (low/high beam or DRL)
Warning message or lamp indicating headlamp or network fault
Loss of adaptive lighting, leveling or auto headlamp functions
Multiple communication-related U-codes stored
Intermittent headlamp operation or flicker
No response from Headlamp Control Module when scanned

What to check

Scan the vehicle with a capable scan tool; note U0241 and any other U-codes
Attempt to communicate with the Headlamp Control Module using the scanner
Inspect fuses and relays related to headlamp and module power
Visually inspect module connector for corrosion, bent pins, or water intrusion
Check battery voltage and charging system (11–14.5 V expected)
Verify good chassis/engine ground and module ground circuit continuity

Signal parameters

CAN bus recessive voltage: ~2.5 V on CANH and CANL (key ON, idle bus)
CAN dominant state: CANH ~3.5 V, CANL ~1.5 V (differential ~2.0 V) during activity
Differential CAN voltage while active: ~1.5–2.5 V depending on bus load
Typical CAN bus termination: ~60 Ω measured between CANH and CANL at two terminators in parallel
Valid module supply: battery voltage between ~11–14.5 V at the HCM power pin with IGN on
Module ground loop resistance: low, typically

Diagnostic algorithm

Record freeze frame data and all stored network fault codes with a scan tool. Note any other U-codes present.
Attempt to communicate directly with Headlamp Control Module A. If it responds intermittently or not at all, proceed.
Check vehicle battery voltage and ensure stable supply (repair/charge if low).
Inspect fuses/relays for headlamp/module circuits; replace any blown fuses and re-test communication.
Visually inspect the HCM connector and harness for corrosion, bent pins, water ingress, insulation damage, or recent repair splices.
Backprobe the module connector: verify constant battery/power feed and switched/IGN feed (where present) and a solid ground reference with key ON.
Measure CANH/CANL voltages with key ON at the module connector. Expect ~2.5 V on each with an idle bus. If voltages are abnormal, trace wiring for short to battery/ground or open circuit.
With a scope (preferred) or multimeter, check for CAN bus activity while cranking/accessory on. Verify proper dominant/recessive transitions and differential voltage. If the bus is silent, isolate which module is missing.
Check CAN termination resistance (~60 Ω). Remove modules as required to isolate a shorted/faulty device that may be pulling the bus down.
Wiggle test harness and connectors while monitoring communication to reproduce intermittent faults—do not wiggle near moving parts or hot components.
If wiring, connectors, or power/ground faults are found, repair or replace damaged wiring or connectors and retest.
If wiring and power/ground check OK but module will not respond, verify module part number and software level; reprogram or replace module per manufacturer procedure if required.