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Home / DTC / B124B — Left daytime running light

B124B — Left daytime running light

Detailed page for trouble code B124B.

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Code

B124B

LAND ROVER B — Body

Left daytime running light

Brand: LAND ROVER
Type: B — Body
Views: UK: 5 EN: 11 RU: 10
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Page language: EN

Causes

  • Failed or degraded DRL lamp (burned-out bulb or failed LED module)
  • Corroded, damaged or disconnected lamp connector or wiring harness
  • Open circuit or short (to ground or battery) in the DRL power or return circuit
  • Blown fuse or faulty relay supplying the DRL circuit
  • Faulty headlamp or lamp control module
  • Body control module (BCM) software/configuration or internal fault

Symptoms

  • Left daytime running light does not illuminate
  • Left DRL flickers or is dim compared with right side
  • Dash warning or lamp message indicating exterior light fault
  • Asymmetric vehicle illumination (one side lit, one side unlit)
  • Possible stored or active fault code B124B in the BCM

What to check

  • Read and record all stored DTCs and freeze-frame data with a capable scan tool; note any related communication or body module codes
  • Visually inspect left headlamp assembly, lens, and wiring harness for damage or water ingress
  • Check relevant fuses and relays for the DRL circuit
  • Operate DRLs and verify behaviour (ignition on / engine running as required)
  • Measure battery voltage at the lamp connector with harness connected and with DRL activated
  • Check ground integrity at the lamp ground point (voltage drop or continuity test)

Signal parameters

  • Supply voltage at lamp connector: ~11–15 V with engine running (varies with system)
  • Control signal may be a switched supply or a PWM control; PWM frequency varies by model—use oscilloscope for verification
  • Expected continuity: low ohms between lamp ground and chassis (
  • LED modules may draw low steady current; current spike/failure indicates internal LED driver fault
  • Scan tool should show DRL status and any module communication — note expected ON/OFF states

Diagnostic algorithm

  1. Use a diagnostic scan tool to read and record DTCs from the BCM and related modules. Clear codes and attempt to re-create to confirm persistence.
  2. Perform a visual inspection of the left headlamp assembly, connectors and wiring for corrosion, damage or signs of water ingress; repair as required.
  3. Verify fuses and relays for the DRL circuit; replace any blown or suspect items and re-test.
  4. With ignition and DRL active, measure battery voltage at the lamp power pin; then measure at the harness side with connector disconnected to isolate lamp vs wiring.
  5. Check ground continuity from lamp ground pin to chassis. Perform a voltage-drop test between ground and battery negative while operating DRL.
  6. If supply and ground are present but lamp does not illuminate, test the lamp itself (replace bulb or swap lamp assemblies where feasible). For LED modules, follow manufacturer test procedure or measure current draw.
  7. If lamp and wiring test OK, inspect BCM or lamp control module outputs using a scope to check for PWM/drive signal. Check for stored BCM faults or communication errors.
  8. Repair or replace failed component (connector/wiring repair, lamp module, fuse/relay, or BCM if confirmed). After repair, clear codes and verify DRL operation over a test drive and multiple ignition cycles.
  9. If intermittent, monitor live data and perform road or vibration tests to reproduce the fault before final repair.

Likely causes

  • Failed LED/DRL lamp module
  • Poor connector contact or wiring damage at the left headlamp
  • Blown fuse or poor power supply to DRL
  • Faulty BCM output or lamp control module
  • Intermittent wiring (chafing/loose pin) causing intermittent fault

Fault status

⚠️ Status
Left daytime running light circuit fault detected. Lamp not operating or control circuit anomaly recorded by the body control module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B124A B124C U0073 U0140 U0100
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