B1BA8

Code

Generic B — Body

Body Control Module Communication Error

Brand: Generic

Type: B — Body

Views: UK: 14 EN: 14 RU: 11

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Page language: EN

Causes

Faulty BCM (internal failure or software fault)
Open, shorted or corroded wiring to BCM (power, ground, communication lines)
Poor or corroded connector pins at BCM or other modules
Loss of module power or ground (intermittent battery voltage)
Network bus fault (CAN/LIN short to voltage/ground, missing termination resistor)
ECU or module producing bus noise or excessive load

Symptoms

Multiple body electrical functions intermittently fail (lock/unlock, lighting, wipers, HVAC control)
Inoperative remote keyless entry or security/immobilizer warnings
Instrument cluster warnings or communication-related messages
Modules not appearing in scan tool or timeout/lost communication entries
Unpredictable vehicle behavior related to convenience/body systems
Possible no-crank/no-start if BCM controls starter/immobilizer

What to check

Read all stored and pending codes from BCM and gateway modules; note freeze-frame and time stamps
Verify BCM power and ground voltages at connector with engine off and key on
Visually inspect BCM and harness connectors for corrosion, bent pins, water ingress, or damage
Scan the vehicle network: confirm BCM appears on bus and check for other U- or B-codes
Measure CAN_H and CAN_L voltages at the BCM connector (key on, engine off) and compare to known idle levels
Check CAN bus termination resistance (~60 ohms across CAN_H and CAN_L with ignition off, no modules connected to bus)

Signal parameters

CAN bus idle (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (common-mode ≈ 2.5 V)
CAN bus dominant: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
Termination resistance: ≈ 60 Ω across CAN_H and CAN_L (two 120 Ω in parallel)
Battery voltage to BCM power pin: nominal 12 V (check during key-on and while symptoms occur)
Ground resistance: low ohms to chassis (
Expected message IDs and frequency: BCM should transmit/receive periodic messages — verify presence with a scope/scan tool

Diagnostic algorithm

Capture all codes from all modules and note the time stamp; clear codes and perform a controlled re-check to reproduce.
Inspect BCM connector and wiring for physical damage, moisture, corrosion or loose terminals. Repair as needed.
Verify supply voltage and ground at the BCM with a DMM. Wiggle harness while monitoring voltage to detect intermittent connections.
Use a scan tool to confirm whether the BCM is present on the network and which messages/IDs are missing. Record which modules report communication faults.
Measure CAN_H and CAN_L at the BCM with key ON, engine OFF. Compare to the expected idle values. If abnormal, trace wiring for short to Vb or ground or open circuit.
With ignition OFF, measure termination resistance across CAN_H and CAN_L at several points to confirm proper termination (~60 Ω).
If voltages are correct but communication is intermittent, use an oscilloscope to view waveform integrity and noise; look for spikes, missing frames, or excessive bus loading.
Isolate the bus by disconnecting non-essential modules or recent aftermarket devices to identify if another device is pulling the bus down.
If wiring and bus checks pass, verify BCM software/firmware level and calibration; perform updates or reprogramming per manufacturer procedure if available.
If all above checks pass and the BCM still fails to communicate, replace the BCM and program/configure it to vehicle specifications. After replacement, re-test full network communication and clear codes.
Document repairs and confirm symptoms resolved over a short road test or extended key cycles to ensure intermittent faults do not return.