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Home / DTC / B2940 — Body Control Module (BCM) Internal Fault

B2940 — Body Control Module (BCM) Internal Fault

Detailed page for trouble code B2940.

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Code

B2940

Generic B — Body

Body Control Module (BCM) Internal Fault

Brand: Generic
Type: B — Body
Views: UK: 3 EN: 2 RU: 1
AI status
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Page language: EN

Causes

  • Corrupt BCM software or corrupted non-volatile memory (EEPROM/flash)
  • Internal BCM hardware failure (processor, I/O drivers, regulators)
  • Intermittent or low battery voltage / power supply issues
  • Damaged connector pins, corrosion, or water ingress at BCM
  • Shorted or open wiring to BCM power/ground or network lines
  • External electrical event (jump start, over-voltage, lightning) damaging the BCM

Symptoms

  • Multiple body electrical functions inoperative or intermittent (locks, lights, wipers, windows)
  • One or more modules report communication errors with BCM
  • Instrument cluster warning lights related to body systems
  • BCM not responding to diagnostic scan tool or slow to respond
  • Unexpected module resets or stored multiple internal fault codes

What to check

  • Read and record all stored DTCs and freeze-frame data from BCM and other modules
  • Verify stable battery voltage (12.6 V+ at rest, >13.5 V when charging) during tests
  • Check BCM power and ground circuits for correct voltage and continuity
  • Inspect BCM connector for bent pins, corrosion, water intrusion, or damage
  • Check fuses, fusible links, and relay circuits feeding BCM
  • Confirm CAN/LIN network health: presence of CAN High/Low and valid bus traffic

Signal parameters

  • VBATT at BCM connector (static and while cranking) — expected near battery voltage
  • Ground resistance from BCM ground terminal to chassis (
  • CAN High/CAN Low idle voltages (~2.5 V) and differential amplitude (~2.5 V peak-to-peak)
  • LIN/wake line levels and activity (if applicable)
  • Module supply rail(s) from internal regulator (if access/testable)
  • Diagnostic communication presence (response to CAN diagnostic requests)

Diagnostic algorithm

  1. Record all codes from BCM and all modules; export report if possible.
  2. Verify and document battery condition and charging system; recharge or load-test battery if low.
  3. Inspect BCM mounting area and connector for moisture, corrosion, damage, or rodent/nesting signs.
  4. Check and verify all fuses/relays powering the BCM; repair any blown or corroded fuse holders.
  5. Measure VBATT and ground at BCM connector; repair wiring or grounds that exceed resistance limits.
  6. Verify continuity and wiring integrity on CAN/LIN bus wires to other modules; repair shorts or opens.
  7. Attempt communication with BCM using a known-good OEM scan tool; note response and any bootstrap/bootloader messages.
  8. Clear codes and attempt to reproduce the malfunction; monitor for reappearance and for related module codes.
  9. If communications are intermittent or software-related, check for available TSBs/firmware updates; perform reflash/reprogram using OEM procedures.
  10. If internal hardware failure is confirmed (no communication, persistent internal-fault codes after power/wiring verified and reflashing attempted), replace BCM with OEM-specified unit and perform required programming/coding and system relearn procedures.
  11. After repairs or replacement, verify all body functions, clear codes, and perform a full network scan to confirm no residual faults.

Likely causes

  • Faulty or corrupted BCM software/firmware
  • Damaged BCM power supply or internal regulator
  • Poor ground or battery connection causing resets and memory errors
  • Connector corrosion or bent pins causing intermittent contact
  • CAN/LIN network fault presenting as internal error in BCM

Fault status

⚠️ Status
Internal Body Control Module fault detected. The module logged an internal hardware/firmware error or communication failure. Verify power, grounds, connectors and network before considering module replacement.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 2 - 6 hours

Similar codes

B2945 B2950 B2800 U0100 U0140 U0121
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