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Home / DTC / U0129 — Lost communication with the brake system control module

U0129 — Lost communication with the brake system control module

Detailed page for trouble code U0129.

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U0129

LAND ROVER U — Network/User

Lost communication with the brake system control module

Brand: LAND ROVER
Type: U — Network/User
Views: UK: 1 EN: 5 RU: 1
AI status
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Page language: EN

Causes

  • Open or short in CAN bus wiring between ABS module and network
  • Failed brake system control module (ABS/Brake ECU)
  • Blown fuse or removed power/ignition feed for the brake module
  • Poor or corroded ground or connector at the brake module
  • BUS-off condition caused by a node repeatedly transmitting errors
  • Faulty gateway/module (BCM/IC) that routes CAN messages

Symptoms

  • Brake warning lamp and ABS warning lamp illuminated
  • Possible reduced braking functions or degraded ABS/ESC availability
  • Loss of related driver-assist functions that use brake data (e.g., traction control)
  • Stored U0129 (and possibly related U-codes) in multiple modules
  • Inability to communicate with the brake module via diagnostics

What to check

  • Read all stored DTCs and freeze frames from all modules to identify related codes
  • Check battery voltage at key on and during cranking (low voltage may cause comms errors)
  • Verify fuses and relay(s) powering the brake module
  • Visually inspect ABS module connector(s) for corrosion, bent pins, water intrusion, or loose terminals
  • Check for other U-codes on the CAN network (gateway/BCM/ECM) to see if network-wide fault exists
  • Check CAN bus termination resistance (~60 ohms total) and continuity of CAN_H and CAN_L

Signal parameters

  • CAN bus nominal voltages: recessive state ~2.5 V on CAN_H and CAN_L (manufacturer-specific)
  • Dominant state differential typically ~1.5–2.5 V between CAN_H and CAN_L
  • Common bus speeds: typically 500 kb/s or 250 kb/s (check Land Rover model-specific spec)
  • Expected ABS module message rates: periodic status messages often 1–100 Hz depending on function (consult factory data)
  • Termination: two 120 Ω resistors in parallel for ~60 Ω total across CAN_H and CAN_L

Diagnostic algorithm

  1. Confirm DTC: connect a diagnostic tester and record U0129 plus any related codes or freeze-frame data.
  2. Check battery and charging system voltage to rule out low-voltage communication issues.
  3. Verify fuses/relays for the brake control module; replace any blown fuses and re-test communications.
  4. Visually inspect and reseat the ABS module connector(s); if corrosion or damage is found, repair or replace connector and pins.
  5. With scan tool, attempt to communicate directly with the ABS module. If no response, check module power and ground pins for proper voltage and continuity to chassis ground.
  6. Measure CAN bus continuity and resistance between CAN_H and CAN_L at multiple points; verify ~60 Ω termination. Look for shorts to battery or ground.
  7. Use an oscilloscope or CAN bus analyzer to view CAN_H and CAN_L signals while attempting communication. Look for missing messages, dominant states, noise, or a bus-off condition from a node.
  8. If a faulty node is suspected, disconnect suspect modules (one at a time) to see when communication is restored. Isolate the bad module or wiring segment.
  9. If the ABS module has proper power/ground and wiring checks out but still won't communicate, consult manufacturer procedures for module reprogramming or replacement.
  10. After repair, clear codes and perform road test and network health check to verify normal communication and no recurrence of U0129.

Likely causes

  • Blown fuse or lost power/ground to the brake module
  • Corroded or disconnected connector at the ABS module
  • Faulty ABS module (internal failure)
  • Open/shorted CAN_H or CAN_L wiring or missing termination
  • Other module on same CAN causing bus error (gateway/BCM)

Fault status

⚠️ Status
Lost communication with Brake System Control Module (ABS). Check CAN bus, power/ground, connectors and module for faults.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-3 hours
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