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Home / DTC / B1104 — Body Control Module Communication Fault

B1104 — Body Control Module Communication Fault

Detailed page for trouble code B1104.

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Code

B1104

Generic B — Body

Body Control Module Communication Fault

Brand: Generic
Type: B — Body
Views: UK: 4 EN: 5 RU: 9
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Page language: EN

Causes

  • Broken, corroded, or loose wiring/connectors to BCM
  • Low or unstable battery/ignition supply voltage to BCM
  • Poor ground(s) at BCM or shared ground points
  • Faulty BCM hardware or internal module failure
  • CAN/LIN bus short to battery/ground or open circuit
  • Missing or damaged bus termination resistor

Symptoms

  • Loss or intermittent operation of lighting, locks, windows, and other body functions
  • Instrument cluster warnings or communication error messages
  • Inability for scan tool to connect to BCM or missing BCM module in network list
  • Blown fuses related to body circuits
  • Remote keyless entry, alarm, or immobilizer anomalies

What to check

  • Verify stored freeze-frame and history codes; scan all modules for related U/B codes
  • Check battery voltage at rest and with ignition on (should be ~12.4–12.8 V at rest, ~13.5–14.8 V when charging)
  • Visually inspect BCM connectors for corrosion, bent pins, water intrusion, or damage
  • Confirm BCM ground(s) are clean, tight, and free of corrosion
  • Use scan tool to attempt communication with BCM; note if intermittent or absent
  • Measure CAN/LIN bus voltages at BCM connector with key on/engine off

Signal parameters

  • CAN bus recessive voltage: both CAN_H and CAN_L near vehicle reference (~2.4–2.6 V) when idle
  • CAN differential voltage: ~0 V recessive, ~1.5 V dominant; waveform present when bus active
  • Typical data rates: 125 kb/s, 250 kb/s, 500 kb/s or manufacturer-specific — verify correct rate
  • LIN bus idle voltage: near battery voltage through pull-up (check manufacturer spec)
  • Module supply voltage at BCM: within ~11–15 V depending on key/engine state
  • Ground potential:

Diagnostic algorithm

  1. Record all current and pending codes from all modules; note conditions when code set and any related U-codes.
  2. Verify battery state of charge and charging system health. Recharge or replace battery if low and recheck.
  3. Visually inspect BCM and harness connectors for corrosion, moisture, damaged wires, or poor pin fit. Repair any damage.
  4. Confirm BCM power and ground circuits: measure battery feed and ignition feed at BCM pins, and verify ground integrity.
  5. With a capable scan tool, attempt to communicate repeatedly with BCM while wiggling harness and applying gentle pressure to connectors to reproduce intermittent faults.
  6. Measure CAN_H and CAN_L voltages at BCM connector with key on; use an oscilloscope or lab scope to verify correct differential waveform and data activity. Check for short to battery/ground or open circuit.
  7. Check for correct bus termination resistance (~60 ohms across CAN H-L with ignition off or per vehicle spec).
  8. If bus short or load suspected, isolate segments by disconnecting nodes or disconnecting accessories until communication is restored, then repair the offending circuit.
  9. Verify software/calibration: check for available BCM software updates or known service bulletins before module replacement.
  10. If wiring, power, grounds, and software verified and the BCM still fails to communicate or exhibits internal faults, consider controlled replacement or reflash of the BCM following manufacturer procedures (back up configurations/codes first).
  11. Clear codes and retest under the same conditions that originally set the code to confirm repair.

Likely causes

  • Corroded or loose connector pins at the BCM
  • Low battery voltage or failing charging system while code set
  • Open or shorted CAN/LIN wiring near BCM
  • Failed BCM due to internal fault after other causes excluded

Fault status

⚠️ Status
Loss or intermittent communication with Body Control Module detected on vehicle network.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

B1100 B1101 B1102 U0100 U0073 U0121
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