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Home / DTC / B29A4 — CAN Bus Communication Error with Battery Sensor Module

B29A4 — CAN Bus Communication Error with Battery Sensor Module

Detailed page for trouble code B29A4.

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Code

B29A4

MITSUBISHI B — Body

CAN Bus Communication Error with Battery Sensor Module

Brand: MITSUBISHI
Type: B — Body
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Damaged or shorted CAN_H/CAN_L wiring between battery sensor and CAN network
  • Corroded, loose or disconnected connector at battery sensor or junctions
  • Failed battery sensor module
  • Loss of module power or ground (battery terminal, fusible link)
  • Missing/incorrect CAN bus termination (open or wrong resistance)
  • Intermittent contact caused by movement or vibration

Symptoms

  • Battery/BMS warning light or message on dash
  • Incorrect or missing state-of-charge (SoC) or battery health readings
  • Charging system faults or reduced charging performance
  • Vehicle may refuse to start or enter limp mode in some systems
  • Loss of related functions logged in other modules (no telemetry)
  • Intermittent faults that clear and reappear with vibration or after restart

What to check

  • Read stored/freeze-frame data and all related CAN communication U-codes with a capable scan tool
  • Visually inspect battery sensor connector, harness, and battery terminals for corrosion, damage, or loose connections
  • Check fuses and power/ground at the battery sensor module
  • Measure CAN bus termination resistance across CAN_H and CAN_L (~60 ohms total) with ignition off
  • Observe CAN_H and CAN_L signals with an oscilloscope while recording bus activity
  • Wiggle test harness/connectors while monitoring communication to reproduce intermittent failures

Signal parameters

  • Recessive level: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (idle)
  • Dominant condition differential voltage typically ≥ 1.5 V - 3.5 V during frames
  • Typical bus termination: ~60 ohms between CAN_H and CAN_L (two 120 Ω terminators in parallel)
  • Expected periodic battery sensor messages: periodic telemetry or response to requests (message IDs vary by model)
  • No excessive noise, flatlines, or distorted waveforms on oscilloscope

Diagnostic algorithm

  1. Connect a professional scan tool. Read and record B29A4 plus any additional codes/U-codes and freeze frame.
  2. Check battery voltage and condition. Ensure battery terminals are clean and tight; verify module supply fuse and ground integrity.
  3. Visually inspect wiring and connectors from battery sensor to nearest junction. Repair any corrosion, pin damage or loose terminals.
  4. With ignition on, measure termination resistance between CAN_H and CAN_L. Replace/restore termination if out of spec (~60 Ω).
  5. Use an oscilloscope or CAN diagnostic tool to view CAN_H and CAN_L while the vehicle is running to confirm valid differential waveforms and message traffic. Identify if the battery sensor is transmitting.
  6. If the battery sensor is silent or message frames are corrupted, back-probe the module power and ground pins to verify correct supply voltages and grounds during operation.
  7. Perform a wiggle test on the wiring and connectors while monitoring comms to find intermittent faults. Repair or replace damaged sections.
  8. If wiring, power and termination are good but communication still fails, replace the battery sensor module and re-test.
  9. After repairs replace/clear codes, cycle ignition, and verify return of normal telemetry and removal of B29A4. Road test if required and re-check for reoccurrence.

Likely causes

  • Corrosion or poor connection at the battery sensor connector or battery terminals
  • Open or short in the local CAN wiring harness near the battery
  • Battery sensor has lost power or ground (blown fuse, disconnected cable)
  • Failed battery sensor electronics
  • CAN bus termination resistor(s) damaged or disconnected

Fault status

⚠️ Status
Lost or unreliable CAN communication with the battery sensor module — messages not received or corrupted. Check wiring, power/ground, termination, and module.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0100 U0073 U0121 U0155
406

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