B3B1A

Code

Generic B — Body

Body Control Module Internal Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 10 EN: 18 RU: 11

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Page language: EN

Multiple body functions intermittent or non‑functional (locks, lights, windows, wipers, interior lamps)
Warning lamps or communications faults displayed on dash
Diagnostic tool cannot communicate with BCM or shows intermittent connection
Modules report lost communication or multiple network-related DTCs
Vehicle may have unpredictable behavior of body systems
Possible parasitic battery drain if BCM stuck awake

Read all stored and pending DTCs from BCM and other modules; note freeze frame data
Check battery voltage (key off and key on) and battery connections
Verify BCM power feed fuses and fusible links are intact
Inspect BCM connector(s) for corrosion, bent pins, water ingress, or damage
Verify engine/chassis/BCM ground points are clean and secure
Verify CAN/LIN bus wiring continuity and look for shorts to battery or ground

Battery/VBATT: ~11–14.8 V with key on; should not drop excessively during cranking
BCM supply pin: near battery voltage when powered; near 0 V when key off (per vehicle design)
Ground resistance: chassis/BCM ground < 0.5 Ω to battery negative
CAN bus recessive voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V
CAN bus dominant voltages: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ~2 V)
Check for stable CAN traffic with expected baud rate (typically 250 kbps or 500 kbps) and normal packet timing

Record the exact code(s) and any freeze-frame or event data from the scan tool.
Verify battery condition and voltage. Recharge or replace battery if low; clean battery terminals.
Inspect BCM fuses, fusible links and power feed circuits for continuity and correct voltage at BCM pins.
Visually inspect BCM connectors and wiring for corrosion, bent pins, water damage or crushed wires; repair as needed.
Verify ground integrity: measure resistance from BCM ground to battery negative (
Check CAN/LIN bus: with key on, measure CAN_H and CAN_L idle voltages and observe waveforms with a scope to detect missing frames, reflections, or bus shorts.
Disconnect non-essential modules one at a time (or isolate suspect modules) to see if the fault clears — helps identify a network-flooding device.
If power/ground and bus wiring are good, attempt to reinitialize or reflash BCM software per manufacturer procedure; follow OEM steps for security and coding.
If the BCM still shows internal communication fault after software reflash and wiring verified, replace the BCM and program/codify into the vehicle per OEM instructions.
After repair, clear DTCs and operate the vehicle to verify issue does not recur; re-scan all modules for related codes.