B1B1C

Code

Generic B — Body

Body Control Module Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 11 EN: 20 RU: 16

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Faulty BCM (internal hardware or software error)
Loss of power or ground to the BCM (blown fuse, poor ground)
Broken, corroded or loose connector pins at the BCM
Open, shorted or high-resistance wiring on CAN or LIN bus
Missing or incorrect network termination resistor(s)
Low battery voltage or unstable supply during communication

Symptoms

Inability to communicate with BCM using a scan tool or intermittent communication
Multiple body systems inoperative or erratic (door locks, lighting, wipers, interior features)
Warning lights or messages related to modules that rely on BCM
Intermittent or persistent network errors stored in other modules
Some modules show 'no communication' (U0xxx) DTCs alongside B1B1C

What to check

Check battery voltage and charging system; ensure stable supply (12.0–14.8 V) during testing
Use a scan tool to read all DTCs from BCM and other modules; note freeze-frame or occurrence data
Attempt to communicate with the BCM; record whether communication is intermittent or absent
Inspect BCM fuses, fusible links and relays related to BCM power
Visually inspect BCM connector for corrosion, bent pins, water intrusion, or mechanical damage
Measure key power and ground terminals at the BCM with connector seated

Signal parameters

Battery voltage at BCM: typically 12.0–14.8 V when engine running
Ground continuity: near 0 ohms from BCM ground to chassis ground
CAN bus idle voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (each), differential ≈ 0 V idle
CAN dominant state voltages (when active): CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈2.0 V)
CAN termination: total approx. 60 ohms across CAN_H and CAN_L with vehicle power on (two 120 Ω in parallel)
LIN bus idle: pulled to battery voltage via master (approx. 12 V when awake) and drops when active

Diagnostic algorithm

Record all DTCs from BCM and other modules and note whether B1B1C is current or history. Attempt communication with BCM using a capable scan tool.
Verify stable battery voltage (12.0 V min, ideally >12.4 V) and good charging system while diagnosing. If low, charge battery or connect a stable power source and retest.
Inspect BCM power and ground circuits: check fuses, relays, fusible links and measure voltage at BCM power pins and ground continuity to chassis.
Visually inspect BCM connector and surrounding wiring for corrosion, water intrusion, damaged insulation, or bent pins. Repair or clean as required.
Measure CAN_H and CAN_L at the BCM connector with ignition on and engine off/ running. Compare to expected signal parameters. If voltages are outside expected ranges, trace wiring for shorts or opens.
Check network termination resistance across CAN_H/CAN_L with vehicle power removed or per service instructions (expect ~60 ohms). Replace missing or damaged termination resistors.
Use an oscilloscope or CAN/LIN analyzer to view bus waveforms and verify proper message traffic, IDs and timing. Look for excessive noise, missing messages, or dominant states.
Disconnect non-essential modules or recent aftermarket additions one at a time (or isolate segments of bus) to determine if a node is pulling down the network.
Wiggle test wiring and connectors while monitoring communication to locate intermittent faults.
If wiring, power and termination check good and communication still fails, verify BCM software/calibration level and perform reflash or reprogramming per manufacturer procedure if required.
If reprogramming does not clear the fault and wiring checks are good, consider BCM replacement; program and configure replacement module per OEM procedure.
Clear codes and perform road/park testing to confirm repair; monitor for reappearance and for related U-codes in other modules.

Likely causes

Poor power or ground at the BCM (fuse, fusible link, ground strap)
Damaged or corroded BCM connector or pin(s)
CAN or LIN wiring fault (short to battery/ground, open, or high resistance)
Failed or incompatible BCM software needing reflash
Faulty BCM (less likely after wiring and power verified)

Fault status

⚠️ Status

Communication fault stored when the Body Control Module fails to send/receive expected messages on the vehicle network or responds with invalid/unavailable data. The condition may be intermittent or permanent and can be caused by power/ground, wiring, termination, or module failure.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours