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Home / DTC / B129A — Local interconnection network bus 'D' Left front sensor front right

B129A — Local interconnection network bus 'D' Left front sensor front right

Detailed page for trouble code B129A.

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Code

B129A

LAND ROVER B — Body

Local interconnection network bus 'D' Left front sensor front right

Brand: LAND ROVER
Type: B — Body
Views: UK: 3 EN: 11 RU: 6
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Page language: EN

Causes

  • Faulty left front sensor (front-right)
  • Open, short, or high-resistance wiring/connector on bus D to the sensor
  • Corroded or water-damaged sensor connector
  • Poor ground or supply to the sensor or local modules
  • Faulty gateway/body control module or LIN driver
  • Missing/incorrect termination or pull-up on the LIN network

Symptoms

  • Parking/ultrasonic sensor or related front sensing function inoperative or disabled
  • Warning or message on dash indicating sensor fault or reduced functionality
  • Intermittent operation of the left-front sensing zone
  • Stored DTC B129A (communication loss on LIN bus D) or related network fault codes

What to check

  • Read all stored and pending codes from all modules and record freeze-frame data
  • Check service information for exact sensor function and connector location
  • Visually inspect left front sensor, harness, and connector for corrosion, damage, moisture, or pin deformation
  • With ignition ON, back-probe the sensor connector and verify supply voltage and ground presence
  • Check continuity between sensor connector and the controlling module for open/shorts
  • Wiggle harness and connector while monitoring for code set or communications to reproduce an intermittent fault

Signal parameters

  • Bus type: Local Interconnect Network (LIN) — single-wire serial bus commonly used for simple sensors/actuators
  • Idle level: typically pulled up to battery voltage when inactive; dominant state is driven low by master/slave (
  • Message behavior: periodic frames while ignition on; sensor should respond within defined timeouts
  • Expected: stable idle voltage near battery voltage with short low pulses when data is transmitted; no continuous low or noisy waveform
  • If using an oscilloscope: look for clean low pulses, correct timing/baud (refer to factory data for exact baud rate)

Diagnostic algorithm

  1. Record all fault codes from all modules and note any related U-/B- codes. Clear codes and attempt to re-run to confirm persistence.
  2. Consult the vehicle-specific wiring diagram/SIM for bus D routing, connector pinout, and related fuses/ground points.
  3. Visually inspect the left front sensor and harness for damage, corrosion or water ingress. Repair or dry and clean connectors as needed.
  4. With ignition ON, back-probe the sensor connector: verify battery feed, reference/ground and the LIN data line idle voltage. Compare to specification.
  5. Check continuity between the sensor connector and the controlling module (body control/gateway) for open/short/high resistance. Repair any damaged wiring or connectors.
  6. Perform a wiggle test on the harness while monitoring live data or codes to find intermittent faults.
  7. If supply and wiring check good, use a diagnostic tool to request sensor data; if no response, substitute a known-good sensor or temporarily connect a bench-tested sensor to confirm sensor failure.
  8. If the fault follows the replacement sensor, replace the sensor. If the fault remains, inspect/replace wiring, connectors, or repair splice points, and test the controlling module LIN driver.
  9. If wiring and sensor prove OK, check for module software updates and reprogram/reinitialise modules as required by the manufacturer.
  10. After repairs, clear codes and road-test or exercise the system to confirm the fault does not return.

Likely causes

  • Corroded/contaminated connector at the left front sensor
  • Damaged harness where it passes through a wheel arch or door hinge area
  • Failed sensor electronics due to moisture ingress
  • Loose or damaged pin in sensor connector
  • Intermittent short to battery or ground caused by chafed wiring

Fault status

⚠️ Status
Communication fault reported: Local Interconnect Network (bus D) - left front sensor (front right) not responding or sending invalid data.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

B129B U0100 U0140 U0155 U0164
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