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Home / DTC / B29D3 — BCM — Rear Door Module Communication Fault

B29D3 — BCM — Rear Door Module Communication Fault

Detailed page for trouble code B29D3.

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B29D3

Generic B — Body

BCM — Rear Door Module Communication Fault

Brand: Generic
Type: B — Body
Views: UK: 0 EN: 0 RU: 0
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Page language: EN

Causes

  • Open, shorted, or intermittent wiring in the door harness (door jamb area)
  • Corroded or loose connector(s) at the rear door module or BCM
  • Loss of module power or ground (fuse, wiring, poor chassis ground)
  • Faulty Rear Door Module or BCM hardware
  • CAN/LIN bus fault (terminations, short to battery/chassis, bus-off)
  • Software/configuration mismatch or corrupted module software

Symptoms

  • Rear door functions inoperative or intermittent (locks, windows, mirror, courtesy lamp)
  • Central locking or keyless entry failure for the affected door
  • Diagnostic tool reports 'No Response' or 'Not Present' for Rear Door Module
  • Related lamps or indicators may be disabled or behave erratically
  • Possible DSM/BCM stored additional communication DTCs (bus timeouts)
  • Intermittent faults that change with door position or movement

What to check

  • Use a scanner to read all related DTCs and freeze frame data; note module presence and timeouts
  • Visually inspect the rear door connector, seals, and wiring through the door hinge area
  • Check fuses and relays supplying the RDM and BCM
  • Backprobe and verify RDM supply voltage (battery/ignition) and ground with key on
  • Wiggle the harness through the door jamb while monitoring communication and functions
  • Scan for other modules showing CAN/LIN bus errors (bus-off, bus passive)

Signal parameters

  • Battery supply to RDM: ~12 V (within nominal battery voltage range; verify with key on/crank as applicable)
  • Ground continuity: low resistance to chassis (
  • CAN bus idle voltages (typical): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V; dominant state CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (verify against vehicle specification)
  • CAN differential waveform: clean edges, correct termination, no excessive noise
  • Expected module heartbeat/telemetry: periodic message (manufacturer-specific; often >=1 Hz) or response to diagnostic request within ~100–500 ms
  • Harness resistance through hinge: continuity with no intermittent opens; typical low ohms (

Diagnostic algorithm

  1. Record all codes and freeze frame data; clear codes and attempt to reproduce the fault to confirm persistence.
  2. Confirm whether the Rear Door Module is present on the network using a scan tool. Note if module responds to diagnostics or is 'Not Present'.
  3. Inspect connectors and wiring at the rear door and BCM for corrosion, bent pins, pushed-out terminals, or water damage. Repair any visible damage.
  4. Verify power and ground at the RDM with backprobe: battery voltage present when required and solid ground. Repair any supply/ground faults.
  5. With a scope or multimeter, observe CAN_H and CAN_L at the RDM connector and at the BCM. Look for proper idle voltages, message activity, and noise. Wiggle wiring through the door hinge while watching for interruptions.
  6. Check fuses/relays for RDM/BCM circuits. Replace blown fuses and investigate cause if fuse reopens.
  7. If CAN lines show short to battery or chassis, isolate by disconnecting sections and using ohmmeter/bench tests. Repair shorts/open circuits and restore proper termination (usually 120 Ω across CAN H/L at network ends).
  8. If wiring, power and grounds are good but module still does not communicate, attempt module reset/reprogramming per manufacturer procedure. Verify software calibration levels are correct.
  9. If available, substitute a known-good RDM (or BCM if indicated) and re-check communication. Do not replace modules until wiring and power/ground are confirmed good.
  10. After repair, clear DTCs and verify proper operation of rear door functions over a test drive/cycle; re-scan for reappearing codes and record results.
  11. Note: Module replacement may require programming or coding; follow manufacturer procedure and secure vehicle immobilizer/anti-theft procedures.

Likely causes

  • Damaged flex cable or broken wires through door hinge (most common for door modules)
  • Poor or corroded connector at RDM or BCM
  • Blown fuse or missing module supply/ignition feed
  • CAN bus wiring shorted or missing termination resistor
  • Failed RDM (module internal fault)
  • BCM software needing update or BCM misconfiguration

Fault status

⚠️ Status
Stored when the Body Control Module detects that the Rear Door Module is not responding to expected network messages or diagnostic requests within the configured timeout. The fault can be active (currently failing) or stored (historical); freeze frame and network status may be recorded to aid diagnosis.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3.0 hours

Similar codes

B29D0 B29D1 B29D2 B29D4 U0100 U0140
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