B125E

Code

Generic B — Body

Body Control Module (BCM) Internal Fault

Brand: Generic

Type: B — Body

Views: UK: 3 EN: 0 RU: 1

AI status

Completed

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Page language: EN

Causes

Internal BCM hardware failure (processor, memory, power regulator)
Corrupted or failed BCM firmware/flash memory
Intermittent or low supply voltage to the BCM
Water intrusion or corrosion of BCM connectors/PCB
Overheating or thermal stress damage
Short circuits or electrical transients (voltage spikes)

Symptoms

One or more body systems fail or operate intermittently (locks, lights, wipers, windows, HVAC controls)
Multiple related B- and U-codes present, or communication errors for BCM
Instrument cluster or other modules show loss of communication with BCM
Random or constant warning lights, incorrect status messages
Vehicle may not enter sleep/wake correctly or shows parasitic drain

What to check

Retrieve all stored and pending DTCs and freeze frame data with a capable scan tool
Verify battery state-of-charge and measure key-on and cranking voltages (11–15 V expected)
Visually inspect BCM connectors and harness for corrosion, water, damage or bent pins
Check ground connection resistance for BCM (low ohms expected)
Measure BCM supply and ground at the module connector under load
Monitor communication bus activity (CAN/LIN) for errors and presence of messages

Signal parameters

Battery/supply voltage at BCM: ~11–15 V (key ON); significant deviations indicate power issues
Ground continuity: low resistance (typically
CAN bus common-mode voltage (quiescent) near mid-supply (~2.5 V); bus differential pulses present during operation
CAN differential amplitude during activity: expected waveform with clear recessive/dominant states
LIN bus idle and message timing (if applicable) — presence/absence of expected frames
Wake/sleep message frequency on bus and any repeated error frames or bus-off conditions

Diagnostic algorithm

Connect a full-function scan tool and record DTCs, freeze frame, and module info (part number, software/firmware version). Check for manufacturer-specific subcodes or history.
Confirm vehicle battery health and charge. Re-test with a fully charged battery or known-good supply to eliminate low-voltage effects.
Visually inspect BCM and surrounding area for signs of water intrusion, corrosion, heat damage, or impact. Check connector seals and tape harness where necessary.
With key ON, measure supply voltage and ground at the BCM connector. If supply is out of range or ground is high resistance, repair wiring/grounds first and retest.
Scan the vehicle bus for communication faults (U-codes). Use a scope or bus analyzer to view CAN/LIN waveforms at the BCM connector — look for noise, missing messages, or bus-off.
If wiring and bus signals are normal, attempt a power-cycle and then a module software reflash or update per manufacturer procedure (ensure correct file and programming tool).
If the code persists after verifying power, ground, wiring, and reflash, consider module-level faults. Confirm with a known-good/replacement BCM when possible and verify required coding/programmings (immobilizer, VIN, configuration).
If replacement BCM is installed, perform all required initialization, coding, and relearns. Re-scan to confirm code resolution and perform functional checks of affected systems.

Likely causes

Failed voltage regulator inside BCM causing unstable internal rails
Corrupted calibration or bootloader preventing normal operation
Physical damage to BCM board (moisture, impact, corrosion)
Loose or corroded power/ground connector at BCM
CAN/LIN transceiver failure inside BCM

Fault status

⚠️ Status

BCM internal fault detected. The module reported an internal hardware or firmware error; associated body functions and module communications may be unreliable or lost.

🔴 Repair difficulty: Hard

⏱️ Diagnostic time: 2.0-4.0 hours