B2940

Code

Generic B — Body

Body Control Module (BCM) Internal Fault

Brand: Generic

Type: B — Body

Views: UK: 18 EN: 15 RU: 18

AI status

Completed

ready

Completed 100%

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

Record all codes from BCM and all modules; export report if possible.
Verify and document battery condition and charging system; recharge or load-test battery if low.
Inspect BCM mounting area and connector for moisture, corrosion, damage, or rodent/nesting signs.
Check and verify all fuses/relays powering the BCM; repair any blown or corroded fuse holders.
Measure VBATT and ground at BCM connector; repair wiring or grounds that exceed resistance limits.
Verify continuity and wiring integrity on CAN/LIN bus wires to other modules; repair shorts or opens.
Attempt communication with BCM using a known-good OEM scan tool; note response and any bootstrap/bootloader messages.
Clear codes and attempt to reproduce the malfunction; monitor for reappearance and for related module codes.
If communications are intermittent or software-related, check for available TSBs/firmware updates; perform reflash/reprogram using OEM procedures.
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.
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