B1A01

Code

Generic B — Body

Body Control Module CAN Bus Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 15 EN: 24 RU: 20

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Page language: EN

Causes

Open, short, or high-resistance wiring in CAN high/low lines
Poor or missing power or ground to the BCM
Failed BCM CAN transceiver or internal module fault
Missing or failed termination resistor(s) on the CAN bus
Another module driving the bus into a bus-off or dominant state
Corroded/loose connectors or water intrusion at BCM/splice points

Symptoms

Loss or intermittent operation of BCM-controlled items (lights, door locks, wipers, courtesy lamps, keyless entry)
Warning messages or incorrect indicators on instrument cluster related to body systems
One or more modules show 'no response' or multiple communication DTCs when scanned
Modules appear to reboot or enter bus-off state intermittently
Possible battery drain or inability to go to sleep if bus is held active

What to check

Read and record all stored DTCs and freeze-frame data from BCM and other modules
Check battery voltage and charging system before starting (should be >12.2 V at rest)
Visually inspect BCM connectors, wiring harness, and nearby splices for damage, corrosion, or moisture
Check fuses and main power/ground connections to the BCM
Measure resistance across CANH and CANL at BCM with ignition off (expect ~60 ohm total if two 120 ohm terminators present)
Use scan tool to monitor CAN bus traffic and note missing or low-frequency expected messages

Signal parameters

CANH/CANL idle voltages: roughly mid-rail (~2.5 V) each (recessive state)
Dominant state voltages: CANH rises and CANL falls (typical differential ~1.5–2.5 V)
Differential CANH–CANL voltage peaks during data (~1.5–2.5 V)
Bus termination resistance: ~60 ohm measured across CANH–CANL with network intact (two 120 ohm terminators in parallel)
Bus bit rate (example values): 500 kbps, 250 kbps or other vehicle-specified rate — verify expected bitrate
Message presence/frequency: periodic 'alive' frames from PCM/BCM/ABS and specific message IDs required by BCM

Diagnostic algorithm

Verify and document code(s), freeze frame, and which network(s) are affected using a capable scan tool.
Check vehicle battery state and ensure stable supply voltage; inspect battery terminals and charging system.
Perform a visual inspection of BCM area, connectors and CAN wiring for physical damage, corrosion or moisture.
Verify BCM power and ground circuits (voltage at supply pin with key on and good ground continuity).
With ignition off, measure resistance across CANH to CANL at the BCM — expect ~60 ohm; if open or very high, trace wiring for open/missing terminator.
With key on, measure CANH and CANL DC voltages at BCM and compare to expected mid-rail and dominant levels while exercising the bus; look for short to battery or ground.
Use an oscilloscope or CAN bus analyzer to view waveforms while scanning bus traffic; look for excessive noise, missing frames, repeated error frames, or a node holding the bus dominant.
Isolate the fault by disconnecting non-essential modules one at a time (start with modules recently serviced) to see if the bus returns to normal; monitor termination and resistance after each disconnect.
If a specific module is identified as faulty, verify its power/ground and connectors before replacing; if BCM is the suspected failed node, confirm transceiver failure with scope or component-level tests.
After repair or wiring fix, clear codes and re-check for reappearance. If BCM replacement is required, follow OEM programming and configuration procedures.
Safety note: avoid shorting CANH to CANL or to battery/ground when probing; use proper test equipment and follow ESD precautions for module handling.

Likely causes

Damaged or shorted CANH/CANL at harness or connector near BCM
Bad BCM ground or supply fuse/open circuit
Failed CAN transceiver inside the BCM
Open or missing 120 ohm termination(s) or improper resistance (~60 ohm measured across CANH-L with both terminators present)
Other control module in bus-off state pulling bus low or high
Recent repair or module replacement left connector pins bent/corroded

Fault status

⚠️ Status

Body Control Module detected an interruption or invalid activity on the CAN network (loss of expected messages or bus errors). Further electrical and network diagnosis is required to locate wiring, termination, or module faults.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5 - 3.5 hours