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Home / DTC / U0242 — Lost Communication With Headlamp Control Module B

U0242 — Lost Communication With Headlamp Control Module B

Detailed page for trouble code U0242.

34,405codes
59brands
11,914generic
22,491specific
All codes P-codes (Powertrain) B-codes (Body) C-codes (Chassis) U-codes (Network/User) Tesla Alerts
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Code

U0242

Generic U — Network/User

Lost Communication With Headlamp Control Module B

Brand: Generic
Type: U — Network/User
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty or missing power/ground to the headlamp control module B
  • Damaged, corroded, or disconnected wiring or connectors (including CAN bus lines)
  • Blown fuse or failed relay supplying the module
  • CAN bus fault (open, short to battery/ground, improper termination)
  • Failed headlamp control module B (internal electronics or firmware)
  • Software or calibration mismatch after module replacement or update

Symptoms

  • Driver information/warning lamp or message about headlamp/module communication
  • Headlamp B inoperative, stuck, flickering, or not responding to controls
  • Reduced or no automatic headlamp function for that side (if applicable)
  • Related systems showing reduced functionality or additional communication DTCs
  • Possible loss of CAN bus messages to other modules (intermittent)

What to check

  • Connect a diagnostic scan tool; read and record U0242 and any related network DTCs
  • Check vehicle battery voltage and charging system (stable 12–14.5 V during test)
  • Visually inspect wiring, connectors, and grommets for damage, corrosion, or water ingress at the module and along harness
  • Verify module power and ground with a multimeter at the module connector
  • Check relevant fuses and relays for the headlamp/module circuit
  • Measure CAN bus voltages and termination resistance (check CANH/CANL idle and dominant voltages and ~60 Ω across bus)

Signal parameters

  • Vehicle battery: nominal 12–14.5 V with engine running
  • CAN bus idle voltages: CANH ≈ 2.5 V, CANL ≈ 2.5 V (approx. equal); dominant state: CANH ≈ 3.5 V, CANL ≈ 1.5 V
  • CAN bus differential (dominant) ≈ 2.0 V; termination resistance ≈ 60 Ω across CANH–CANL
  • Module power pin ≈ battery voltage with ignition ON; ground pin ≈ 0 V
  • Expected message frequency: periodic headlamp status messages typically repeat (varies by manufacturer) — absence indicates lost comms

Diagnostic algorithm

  1. Use a scan tool to confirm U0242 and note any additional U0xxx or B/C/P codes. Record freeze-frame and occurrence conditions.
  2. Verify battery voltage is within specification. Low voltage can cause network and module faults.
  3. Visually inspect the headlamp control module B and harness for damage, corrosion, moisture, or loose connectors. Repair or secure connectors as needed.
  4. Check and verify fuses/relays that feed the headlamp control module; replace if blown.
  5. With ignition ON, measure power and ground at the module connector. Repair any open or high-resistance circuits.
  6. Measure CANH and CANL at the module connector with a multimeter/scope. Confirm idle and dominant levels and check for ~60 Ω termination. If voltages are out of range, trace wiring toward the bus and inspect for shorts or opens.
  7. If bus voltages are normal, use a scope or capable scan tool to look for valid CAN frames from module B. If no frames, inspect module-side wiring and connector pins for continuity to the bus and other nodes.
  8. Perform wiggle and connector cleaning tests while monitoring the network for changes. Repair or replace damaged wiring/harness sections.
  9. If a single module is causing bus errors (bus-off), disconnect the module (if safe and recommended by manufacturer) to see if network returns to normal. Use caution with lamps that use high-voltage drivers; isolate power before disconnecting.
  10. If wiring, power, and bus appear good but the module does not communicate, consult manufacturer service information for reprogramming or module replacement. Replace the module only after verifying wiring and network integrity.
  11. Clear codes and perform a road/test verification of the system. Re-scan to confirm resolution.

Likely causes

  • Loose/corroded connector at headlamp control module B
  • Open or shorted CAN-H or CAN-L wiring near the module
  • Blown module fuse or bad power feed
  • Module has entered bus-off state due to repeated errors
  • Module internal failure after water intrusion or impact

Fault status

⚠️ Status
Lost communication with Headlamp Control Module B — module not responding on vehicle network (CAN).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

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Code

U0242

HYUNDAI U — Network/User

Lost Communication With Headlamp Control Module “B”

Brand: HYUNDAI
Type: U — Network/User
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty or missing power/ground to the headlamp control module B
  • Damaged, corroded, or disconnected wiring or connectors (including CAN bus lines)
  • Blown fuse or failed relay supplying the module
  • CAN bus fault (open, short to battery/ground, improper termination)
  • Failed headlamp control module B (internal electronics or firmware)
  • Software or calibration mismatch after module replacement or update

Symptoms

  • Driver information/warning lamp or message about headlamp/module communication
  • Headlamp B inoperative, stuck, flickering, or not responding to controls
  • Reduced or no automatic headlamp function for that side (if applicable)
  • Related systems showing reduced functionality or additional communication DTCs
  • Possible loss of CAN bus messages to other modules (intermittent)

What to check

  • Connect a diagnostic scan tool; read and record U0242 and any related network DTCs
  • Check vehicle battery voltage and charging system (stable 12–14.5 V during test)
  • Visually inspect wiring, connectors, and grommets for damage, corrosion, or water ingress at the module and along harness
  • Verify module power and ground with a multimeter at the module connector
  • Check relevant fuses and relays for the headlamp/module circuit
  • Measure CAN bus voltages and termination resistance (check CANH/CANL idle and dominant voltages and ~60 Ω across bus)

Signal parameters

  • Vehicle battery: nominal 12–14.5 V with engine running
  • CAN bus idle voltages: CANH ≈ 2.5 V, CANL ≈ 2.5 V (approx. equal); dominant state: CANH ≈ 3.5 V, CANL ≈ 1.5 V
  • CAN bus differential (dominant) ≈ 2.0 V; termination resistance ≈ 60 Ω across CANH–CANL
  • Module power pin ≈ battery voltage with ignition ON; ground pin ≈ 0 V
  • Expected message frequency: periodic headlamp status messages typically repeat (varies by manufacturer) — absence indicates lost comms

Diagnostic algorithm

  1. Use a scan tool to confirm U0242 and note any additional U0xxx or B/C/P codes. Record freeze-frame and occurrence conditions.
  2. Verify battery voltage is within specification. Low voltage can cause network and module faults.
  3. Visually inspect the headlamp control module B and harness for damage, corrosion, moisture, or loose connectors. Repair or secure connectors as needed.
  4. Check and verify fuses/relays that feed the headlamp control module; replace if blown.
  5. With ignition ON, measure power and ground at the module connector. Repair any open or high-resistance circuits.
  6. Measure CANH and CANL at the module connector with a multimeter/scope. Confirm idle and dominant levels and check for ~60 Ω termination. If voltages are out of range, trace wiring toward the bus and inspect for shorts or opens.
  7. If bus voltages are normal, use a scope or capable scan tool to look for valid CAN frames from module B. If no frames, inspect module-side wiring and connector pins for continuity to the bus and other nodes.
  8. Perform wiggle and connector cleaning tests while monitoring the network for changes. Repair or replace damaged wiring/harness sections.
  9. If a single module is causing bus errors (bus-off), disconnect the module (if safe and recommended by manufacturer) to see if network returns to normal. Use caution with lamps that use high-voltage drivers; isolate power before disconnecting.
  10. If wiring, power, and bus appear good but the module does not communicate, consult manufacturer service information for reprogramming or module replacement. Replace the module only after verifying wiring and network integrity.
  11. Clear codes and perform a road/test verification of the system. Re-scan to confirm resolution.

Likely causes

  • Loose/corroded connector at headlamp control module B
  • Open or shorted CAN-H or CAN-L wiring near the module
  • Blown module fuse or bad power feed
  • Module has entered bus-off state due to repeated errors
  • Module internal failure after water intrusion or impact

Fault status

⚠️ Status
Lost communication with Headlamp Control Module B — module not responding on vehicle network (CAN).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0241 U0140 U0100 U0073
371

Browse 371 HYUNDAI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

HYUNDAI

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
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Code

U0242

LAND ROVER U — Network/User

Lost communication with headlight control module B

Brand: LAND ROVER
Type: U — Network/User
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty or missing power/ground to the headlamp control module B
  • Damaged, corroded, or disconnected wiring or connectors (including CAN bus lines)
  • Blown fuse or failed relay supplying the module
  • CAN bus fault (open, short to battery/ground, improper termination)
  • Failed headlamp control module B (internal electronics or firmware)
  • Software or calibration mismatch after module replacement or update

Symptoms

  • Driver information/warning lamp or message about headlamp/module communication
  • Headlamp B inoperative, stuck, flickering, or not responding to controls
  • Reduced or no automatic headlamp function for that side (if applicable)
  • Related systems showing reduced functionality or additional communication DTCs
  • Possible loss of CAN bus messages to other modules (intermittent)

What to check

  • Connect a diagnostic scan tool; read and record U0242 and any related network DTCs
  • Check vehicle battery voltage and charging system (stable 12–14.5 V during test)
  • Visually inspect wiring, connectors, and grommets for damage, corrosion, or water ingress at the module and along harness
  • Verify module power and ground with a multimeter at the module connector
  • Check relevant fuses and relays for the headlamp/module circuit
  • Measure CAN bus voltages and termination resistance (check CANH/CANL idle and dominant voltages and ~60 Ω across bus)

Signal parameters

  • Vehicle battery: nominal 12–14.5 V with engine running
  • CAN bus idle voltages: CANH ≈ 2.5 V, CANL ≈ 2.5 V (approx. equal); dominant state: CANH ≈ 3.5 V, CANL ≈ 1.5 V
  • CAN bus differential (dominant) ≈ 2.0 V; termination resistance ≈ 60 Ω across CANH–CANL
  • Module power pin ≈ battery voltage with ignition ON; ground pin ≈ 0 V
  • Expected message frequency: periodic headlamp status messages typically repeat (varies by manufacturer) — absence indicates lost comms

Diagnostic algorithm

  1. Use a scan tool to confirm U0242 and note any additional U0xxx or B/C/P codes. Record freeze-frame and occurrence conditions.
  2. Verify battery voltage is within specification. Low voltage can cause network and module faults.
  3. Visually inspect the headlamp control module B and harness for damage, corrosion, moisture, or loose connectors. Repair or secure connectors as needed.
  4. Check and verify fuses/relays that feed the headlamp control module; replace if blown.
  5. With ignition ON, measure power and ground at the module connector. Repair any open or high-resistance circuits.
  6. Measure CANH and CANL at the module connector with a multimeter/scope. Confirm idle and dominant levels and check for ~60 Ω termination. If voltages are out of range, trace wiring toward the bus and inspect for shorts or opens.
  7. If bus voltages are normal, use a scope or capable scan tool to look for valid CAN frames from module B. If no frames, inspect module-side wiring and connector pins for continuity to the bus and other nodes.
  8. Perform wiggle and connector cleaning tests while monitoring the network for changes. Repair or replace damaged wiring/harness sections.
  9. If a single module is causing bus errors (bus-off), disconnect the module (if safe and recommended by manufacturer) to see if network returns to normal. Use caution with lamps that use high-voltage drivers; isolate power before disconnecting.
  10. If wiring, power, and bus appear good but the module does not communicate, consult manufacturer service information for reprogramming or module replacement. Replace the module only after verifying wiring and network integrity.
  11. Clear codes and perform a road/test verification of the system. Re-scan to confirm resolution.

Likely causes

  • Loose/corroded connector at headlamp control module B
  • Open or shorted CAN-H or CAN-L wiring near the module
  • Blown module fuse or bad power feed
  • Module has entered bus-off state due to repeated errors
  • Module internal failure after water intrusion or impact

Fault status

⚠️ Status
Lost communication with Headlamp Control Module B — module not responding on vehicle network (CAN).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0241 U0140 U0100 U0073
320

Browse 320 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

LAND ROVER

Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email

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