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Home / DTC / B123A — Signal of left turn left

B123A — Signal of left turn left

Detailed page for trouble code B123A.

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Code

B123A

LAND ROVER B — Body

Signal of left turn left

Brand: LAND ROVER
Type: B — Body
Views: UK: 4 EN: 13 RU: 8
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Page language: EN

Causes

  • Failed/incorrect bulb or LED module
  • Open, short or high resistance in wiring to left turn lamp
  • Poor or corroded ground or connector at lamp
  • Blown fuse or faulty relay (if fitted)
  • Body Control Module (BCM) or dedicated lighting module fault
  • Intermittent CAN/LIN communication or software fault

Symptoms

  • Left turn lamp does not illuminate when selected
  • Left turn lamp flickers, is dim or flashes rapidly (hyperflash)
  • Amber turn indicator on dash shows error or does not match lamp operation
  • Intermittent operation of left indicator
  • Related communications warnings may appear (loss of module)

What to check

  • Read all stored and pending DTCs from all modules (BCM, instrument cluster, gateway) and note freeze frame/occurrence conditions
  • Visually inspect left turn lamp (bulb or LED), lens, housing and connectors for damage or corrosion
  • Check fuses/relays related to exterior lamps
  • With turn signal activated, verify lamp illuminates (or not). Replace bulb with known good lamp if applicable
  • Measure supply voltage at lamp connector while activated and check ground continuity
  • Inspect wiring harness for chafing, pinched or damaged wires between lamp and BCM

Signal parameters

  • Expected supply voltage at lamp connector: approx 11–14 V when turn signal activated
  • Expected ground continuity: near 0 Ω (vehicle off) to
  • Typical flash rate: ~1 Hz (60–120 flashes per minute) for normal operation; rapid flashing indicates open/failed bulb or high resistance
  • LED modules may present higher resistance and are driven by BCM/lamp driver — current signature differs from incandescent bulbs
  • CAN/LIN: control messages present between BCM and lamp module (if applicable) — check for valid IDs and normal traffic

Diagnostic algorithm

  1. Confirm customer concern and attempt to reproduce fault (engine on/off, different selector positions).
  2. Scan vehicle with manufacturer-level scan tool. Record B123A and any related codes; check freeze frame and module voltage. Clear codes and attempt to re-produce.
  3. Visually inspect left lamp assembly, bulb/LED and connector for corrosion, damage or moisture. Replace bulb with known good unit if incandescent.
  4. Check related fuses/relays. Replace if blown and re-test. If fuse repeatedly blows, stop and trace cause.
  5. With turn signal activated, probe lamp connector: verify +12V feed and ground. If no voltage, trace back toward BCM/relay. If voltage present and lamp does not light, suspect lamp assembly or ground.
  6. Perform continuity/resistance checks between BCM output pin and lamp connector ground; repair any open/short. Wiggle harness to check for intermittent faults.
  7. If vehicle uses a separate lamp driver module or smart LED module, check module supply, grounds and communications (CAN/LIN). Verify module responding on network using scan tool.
  8. If wiring and lamp check good and module communications present, check BCM outputs with scope for expected pulsed signal. Compare with known-good values.
  9. If BCM or lamp driver is suspected, verify software/firmware level and technical service bulletins. Reprogram or replace module per manufacturer procedure if required.
  10. After repairs, clear codes and road-test. Re-scan to ensure B123A does not return.

Likely causes

  • Burnt-out/failed left turn lamp (bulb or LED)
  • Corroded or loose connector at left lamp
  • Open/short in turn lamp feed or ground circuit
  • Faulty BCM or lamp driver module

Fault status

⚠️ Status
Left turn signal circuit fault detected (B123A). Check lamp, wiring, connectors and control module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2 hours

Similar codes

B123B B124A B1230 U0155 U0100
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