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Home / DTC / B1A68 — Body Control Module (BCM) CAN Bus Communication Fault

B1A68 — Body Control Module (BCM) CAN Bus Communication Fault

Detailed page for trouble code B1A68.

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B1A68

Generic B — Body

Body Control Module (BCM) CAN Bus Communication Fault

Brand: Generic
Type: B — Body
Views: UK: 0 EN: 2 RU: 0
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Page language: EN

Causes

  • Damaged CAN bus wiring (open, short to ground or battery)
  • Corroded or loose BCM connector or pins
  • Poor or missing ground or battery supply to BCM
  • Failed or intermittent Body Control Module
  • Another module on the CAN network is pulling the bus down
  • Missing or incorrect CAN termination resistor

Symptoms

  • No response or limited response from BCM on a scan tool
  • Multiple body systems inoperative (lights, locks, windows, wipers)
  • Intermittent or permanent loss of convenience features (keyless entry, dome lights)
  • Dashboard warnings for modules or CAN communication
  • Other modules reporting 'lost communication with BCM'
  • Possible abnormal battery drain or failure to wake from sleep

What to check

  • Connect an OEM-level scan tool and attempt to communicate with the BCM. Record related U-codes and freeze frame data.
  • Check vehicle battery voltage (should be ~12.6 V at rest) and charging system health.
  • Visually inspect BCM connectors and harness for corrosion, bent pins, water intrusion, or mechanical damage.
  • Check fuses and power/ground circuits for the BCM.
  • Measure CAN‑H and CAN‑L voltages at the BCM connector with key on (see signal_params).
  • Check continuity and resistance of CAN‑H and CAN‑L between BCM and other network nodes; check for shorts to ground or battery.

Signal parameters

  • Typical voltages (varies by vehicle): Recessive state: CAN‑H ≈ 2.5 V, CAN‑L ≈ 2.5 V
  • Dominant state: CAN‑H ≈ 3.5 V, CAN‑L ≈ 1.5 V (differential ≈ 2 V)
  • Idle differential voltage should be near 0 V between nodes in recessive state, measured as CAN‑H ≈ CAN‑L ≈ 2.5 V
  • Termination: two 120 Ω resistors in parallel (one at each end) → ~60 Ω measured across CAN‑H and CAN‑L at a single point
  • Common CAN speeds: 250 kbps or 500 kbps (verify vehicle spec before waveform analysis)
  • Expected behaviour: stable square/bit waveforms on scope; excessive noise, dominant stuck levels, or distorted edges indicate wiring/module faults

Diagnostic algorithm

  1. Record DTC and any freeze frame data. Clear codes and attempt to re-create to confirm consistency.
  2. Verify battery and charging voltages, inspect BCM power and ground circuits and fuses.
  3. Attempt to communicate with BCM using a scan tool. Note 'no response' or partial response and check whether other modules can see the BCM.
  4. Visually inspect BCM connector, pins and harness. Repair any corrosion, bent pins or damaged insulation before further testing.
  5. Backprobe CAN‑H and CAN‑L at the BCM with an accurate multimeter: confirm recessive voltages ~2.5 V, then monitor while key/ignition cycles to observe changes.
  6. Measure termination resistance across CAN‑H and CAN‑L. If not ~60 Ω, locate missing/failed terminator(s) or open splices.
  7. Use an oscilloscope to view CAN waveforms at BCM and at a known-good node; compare wave shapes, amplitude, and timing to identify fault location or noisy segments.
  8. Isolate sections of the network if necessary: disconnect suspect modules one at a time (with proper service procedure) while monitoring the bus to see when communication is restored.
  9. Repair wiring, connectors, grounds, or replace faulty module(s) as indicated by tests. Replace BCM only after wiring and bus integrity are confirmed.
  10. After repairs, clear codes, verify communication with scan tool, and perform functional checks of affected systems. Reprogram/configure replaced modules per manufacturer procedure.

Likely causes

  • Loose/corroded connector at the BCM
  • Short or high resistance in CAN‑H or CAN‑L between BCM and network
  • Failed BCM
  • Faulty termination (open or incorrect resistor)
  • Another module fault affecting bus communication

Fault status

⚠️ Status
BCM CAN bus communication fault — Body Control Module not communicating properly on vehicle CAN network.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 1.0-4.0 hours

Similar codes

U0073 U0100 U0121 B1A67 B1A69
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