B1D54

Code

Generic B — Body

Body Control Module CAN Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 12 EN: 9 RU: 11

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Causes

Open, shorted or damaged CAN bus wiring or connectors (BCM network segment)
Intermittent or poor ground or battery supply to the BCM
Failed BCM internal CAN transceiver or other internal BCM hardware fault
Failed or misconfigured gateway or another module flooding or holding the bus
Blown fuse or faulty ignition/power supply circuit to BCM
Corrosion, water ingress or mechanical connector damage

Symptoms

One or more body functions (locks, interior lights, wipers, HVAC controls) intermittent or inoperative
Instrument cluster warnings about module communication or multiple modules not communicating
Stored communication-related DTCs (other U- or B-codes) appearing
Intermittent or permanent no-start or immobilizer-related issues if BCM controls security
Unusual CAN bus traffic, bus-off events, or ECU lamp illumination
Multiple erroneous or disappearing module messages on a scan tool

What to check

Connect a scan tool and record all stored/active DTCs and freeze-frame data; note time stamps and ignition state
Check battery voltage and charging system; verify stable supply (12.0–14.5 V) during tests
Visually inspect BCM connector(s) and CAN wiring for damage, corrosion, water ingress, pin push-out, or aftermarket splices
Check BCM fuses and relays for proper condition and power feed continuity
Check chassis and engine ground points related to BCM for tightness and corrosion
Use an oscilloscope or DVM to measure CAN_H and CAN_L voltages at the BCM connector with key ON and during activity

Signal parameters

Idle CAN_H ≈ 2.5 V and CAN_L ≈ 2.5 V (approximately half-battery) on high-speed CAN
Dominant state typical voltages: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (values are manufacturer-dependent)
Bus differential when idle ≈ 0 V, differential when dominant ≈ 2.0 V (typical)
Expected bus termination resistance across CAN_H and CAN_L ≈ 60 ohms (two 120 Ω in parallel) for a single high-speed network
Message rates vary by module; BCM messages often transmit periodically (tens to hundreds of ms); look for gaps or collisions
Look for excessive error frames, bus-off conditions, or a single node holding the bus dominant

Diagnostic algorithm

Read and document all DTCs and related data with a capable scan tool. Check for supporting U-codes and time-of-occurrence.
Verify battery voltage and ground integrity. Recharge or stabilize battery if low before further testing.
Inspect BCM connector, pins and wiring for corrosion, bent pins, signs of water intrusion, or recent repair/aftermarket splices.
Check BCM power and ground circuits for continuity and correct voltage at the BCM connector (key ON). Replace blown fuses or faulty relays.
With key ON, monitor CAN_H and CAN_L at the BCM. Use an oscilloscope to confirm idle and dominant voltages and to look for noise, missing frames, or bus contention.
Measure termination resistance across CAN_H and CAN_L with power off. Expected ≈ 60 Ω; large deviations indicate missing or additional termination.
If a misbehaving node is suspected, disconnect non-critical modules one at a time (per wiring diagrams) to identify a module causing bus contention. Monitor the bus after each disconnect.
Inspect and, if necessary, repair or replace damaged wiring or connectors. Secure grounds and reseal any locations where water ingress occurred.
If wiring and power/grounds check good and the bus behaves normally with the BCM disconnected (or isolation points used), consider BCM replacement or bench diagnostics. Confirm programming or calibration levels before replacement.
After repairs, clear DTCs, verify communications with the scan tool, and perform a full system check to ensure no other modules are affected. If codes return, consult manufacturer technical service information for module-specific tests and software updates.