B2671

Code

Generic B — Body

Body Control Module Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 6 EN: 7 RU: 2

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Page language: EN

Multiple body functions inoperative or intermittent (lights, wipers, door locks, windows, HVAC controls)
Illumination of multiple warning lamps or communication warnings on dash
Remote keyless entry, immobilizer, or alarm not functioning
No response from BCM-controlled modules when commanded
Other modules report 'lost communication' DTCs

Read all stored and pending codes from BCM and other modules with a capable scan tool and record freeze-frame data
Verify battery voltage is stable (nominal 12.4–12.8 V at rest; >13.5 V when charging) and test state of charge
Inspect BCM fuses and fusible links for continuity
Visually inspect BCM connector(s) and harness for corrosion, bent pins, water damage, or chafing
Check for other modules reporting communication loss (helps localize bus segment)
Look for recent aftermarket installations (alarms, audio, trackers) that tap the CAN or power circuits

Presence and frequency of CAN bus messages (kHz or messages/sec) on high and low lines
CAN bus voltage levels: idle differential voltage and individual wire voltages
LIN bus activity and wake pulses (if applicable)
BCM supply voltage (VBATT) and ground continuity
Module wake/sleep state messages and timeouts
Diagnostic message response time and packet error counts

Connect a factory-level or bi-directional scan tool. Read all DTCs stored in BCM and other control modules; note timestamps and freeze-frame data.
Check battery voltage and charging system. Recharge or replace battery if low and re-check codes after stable voltage.
Verify BCM fuses and power/ground circuits for proper continuity and correct voltages at the BCM connector with key ON and engine OFF.
Inspect BCM connector and wiring harness for corrosion, damage, bent pins or water intrusion. Repair any physical damage.
Using a scope or bus monitor, verify CAN (and LIN if used) physical layer signals at the BCM connector: proper idle voltages, differential signal, and presence of messages from other modules.
If bus signals are absent at BCM but present elsewhere, trace wiring between BCM and bus backbone for open/short/poor splice. Repair wiring as required.
If intermittent, perform wiggle tests on harness and connectors while monitoring bus traffic and DTC status to reproduce the fault.
Check for interfering aftermarket devices by disconnecting them and rechecking communication.
If wiring and power/ground are confirmed good and bus traffic still shows no valid BCM messages, attempt BCM software reflash or perform recommended resets per manufacturer procedures.
Replace BCM only after confirming fault persists with correct power, ground and bus wiring; program/configure new module per manufacturer instructions and verify operation.